1  The Mixed Arbitral Tribunals (‘MATs’) (Tribunaux Arbitraux Mixtes, Tribunali Arbitrali Misti, Mieszane Trybunały Rozjemcze, Gemischte Schiedsgerichte, Vegyes döntőbíróságok, Смесени арбитражни съдилища, Μικτά Διαιτητικά Δικαστήρια‎, Karma Hakem Mahkemeleri) were international arbitration bodies established by the Paris peace treaties of 1919–20 between the Allies and the former Central Powers (Art 304 Treaty of Versailles with Germany (28 June 1919) (‘TV’) (Versailles Peace Treaty (1919)); Art 256 Treaty of Saint-Germain with Austria (10 September 1919) (‘TSG’); Art 188 Treaty of Neuilly with Bulgaria (27 September 1919) (‘TN’); Art 239 Treaty of Trianon with Hungary (4 June 1920) (‘TT’); and later Art 92 Treaty of Lausanne with Turkey (24 July 1923); similar provisions were also included in the Treaty of Sèvres with Turkey (10 August 1920), which was however never ratified (Arts 311–12) (Peace Treaties After World War I)).

2  The main objective of the MATs was to decide the disputes regarding the treatment of private rights according to these peace treaties. This ‘self-standing court system’ (Isidro and Hess, 2019, 242) functioned for around 20 years (1920–39). The MATs ‘most radical characteristic’ (compared to earlier international tribunals) was ‘that not only States but also private individuals may appear before them as parties’ (de Auer, 1927, xvii) (Individuals in International Law). For contemporaries, the MATs thus formed ‘an entirely new jurisdiction’ (‘une juridiction entièrement nouvelle’ [translation by the author]) with massive influence on post-First World War reparations regimes and the national economies throughout Europe and beyond (Gidel and Barrault, 1921, 325; see Fauchille, 1921, 1042; war reparations). For ease of reference, the following entry will focus on the MATs with German participation according to the TV as these MATs dealt with the vast majority of cases handled by all MATs and also the scholarly literature of the time focused on those MATs with German participation.

3  Based on special wartime legislation and economic nationalist ideas, during the First World War private property of ‘enemy aliens’ had been requisitioned, confiscated, sequestrated, and liquidated by governments throughout the world. The notion that private property, irrespective of the nationality of the proprietor or a state of war, was to be held ‘inviolable’ (‘[p]rivate property cannot be confiscated’, Art 46 Annex to IV Hague Convention of 1907) was replaced by considerations that property can be turned into a central instrument for state power, making property a privilege for some, not a fundamental right for all (Borchard, 1924, 523; Gosewinkel, 2014, 24). Often justified as acts of retaliation and hoping to weaken the economic capacity of the enemy, since 1914 national bureaucracies set up for this purpose seized, controlled, confiscated, and liquidated properties and assets (factories, banks, real estate, cars, ships, infrastructure and networks, capital invested in businesses, shares, bank accounts, patents, trademarks, or personal possessions) belonging to enemy aliens found in their respective territories. For example, under the Trading with the Enemy Amendment Act 1914 the Board of Trade appointed the Public Trustee to be the custodian of enemy property in England and Wales.

4  Since 1916, the Reichskommissar für die Liquidation ausländischer Unternehmungen showed Germany’s equal intention to make use of enemy property (Rocholl, 1921, 571). Deeply impacting international public and private law, over the war years such ‘nostrification’ measures, forming part of the ‘economic war’, enticed new legal expertise on all norms concerning enemy alien private property located in national territory or private property in occupied enemy territory, on war damages and their reparations, or on debts and credits. Moreover, jurists considered the effects of the war on contracts, debating, for example, the nature of force majeure (non-payment of debts) or governmental interference in the freedom of contract (Caglioti, 2014; Deroussin, 2014). Considering the previously unheard of connection between the enjoyment of property rights and nationality status created by wartime legislation, Fauchille (1921, 1043) declared after the war that ‘the private rights were infringed during the world war … more than in any other war’ (‘droit privés ont été atteints dans la guerre mondiale … plus que dans toute autre guerre’ [translation by the author]).

5  In light of the heavy damage in Allied territories caused by the war, the confiscation, sequestration, and liquidation of Allied properties and assets in Central Powers territories, and ‘war measures’ such as the internment of Allied civilians by the Central Powers, Allied governments agreed among themselves on a broad definition of ‘reparations’. Given the public pressure—‘the boche [Germans] will pay for everything’ (‘le boche payera tout’[translation by the author])—they aimed at including not only damage to (private) property but (as far as possible) the entire costs of the war, such as the pensions of soldiers, widows, and orphans. In June 1919, after the Germans had complained about the draft peace treaty, Allied governments reminded them that ‘justice … is the only possible basis for the settlement of the accounts of this terrible war … [and] reparation for wrongs inflicted is of the essence of justice’ (cited in Hull, 2014, 10). In order to start the reconstruction of Allied territories destroyed by the German army, Germany had to replace destroyed properties through the supply of construction materials, agricultural implements, livestock, coal, chemicals, vessels, machinery, etc to the Allies (Annex IV to Part VIII TV, Reparation).

6  Placed at the beginning of Part VIII TV (‘reparations’), Article 231 was designed to stipulate the overall ‘responsibility of Germany and her allies for causing all the loss and damage’ suffered by Allied governments and nationals and the obligation to repair this damage. But Article 232 TV narrowed German responsibility to ‘compensation for all damage done to the [Allied] civilian population … and to their property during the period of belligerency’. With regard to the regulation of the economic consequences of the war (Part X ‘economic clauses’, Arts 264–312 TV), the one-sided model created by the TV was that the Allied governments ‘reserve[d] the right to retain and liquidate all property, rights and interests [within their territories] belonging … to German nationals’ (Art 297 (b) TV) in order to raise money to compensate their own nationals for damage and losses caused by the war (Cauwès and Chaudun, 1921). Germany, on the other hand, was obliged to restore the property, rights, and interests of Allied nationals and had to compensate her own nationals whose property had been confiscated and liquidated by the Allies. Germany was also responsible for paying compensation to Allied proprietors expropriated in Germany during the war. ‘The claims made in this respect by … [Allied] nationals shall be investigated, and the total of the compensation shall be determined by the Mixed Arbitral Tribunal’ (Art 297 (e) TV). As for the debts resulting from pre-war contracts between Allied and Central Power nationals, all open claims had to be settled ‘through the intervention of Clearing Offices [Ausgleichsämter] to be established by each of the High Contracting Parties’ (Art 296 TV). The latter provisions about the establishment of entirely new institutions underlined that the claims settlement of private property and assets affected by the war was distinct from the reparation payments to be paid directly by Germany to Allied governments, the amount of which was to be determined in the future by a ‘reparation commission’ (until May 1921, Art 233 TV) (Reparation Commission (Versailles Treaty)). However, smaller Allied nations like Portugal that had been awarded only minuscule percentages of the overall German reparation payments, hoped to use legal means to gain a larger financial share of what had been denied to them during the inter-Allied diplomatic negotiations.

7  Subsequently, around the world Allied governments requested their nationals (at times including so-called ‘natives’ in the colonies) to list their war-related property damage to be claimed from the German government (for the example of Portuguese-Angola, Zollmann, 2016, 248). For this purpose, they set-up specific administrations (Office of the Custodian of Enemy Property or Clearing House or Office); for instance, in Canada creditors had six months following the promulgation of the Treaty of Peace (Germany) Order (1920) to notify the Clearing Office of their claim (Robert-Moore, 1986, 96; see Charteris 1921).

8  Among contemporary legal scholars and practitioners, the development of interstate arbitration as a means of international dispute resolution based on public international law was a much debated and well-known topic. The practicability of this tool of juridification of disputes between States by a law-based and binding decision of a neutral third party had been proven several times in the decades prior to the First World War (Zollmann, 2018, 118). The term Tribunal Arbitral Mixte—indicating that the tribunal be composed not only of arbitrators of one or several neutral third party States, but also of nationals of the disputing parties—had been in use since the late 19th century; though mostly in domestic (labour) disputes (Saint-Georges, 1890, 10).

9  Given that during the war German and Austrian courts had often denied standing to Allied nationals objecting to the confiscation of their private property, Allied governments refused to entrust to the jurisdiction of the former Central Powers the implementation of the rather one-sided ‘economic clauses’ of their respective peace treaties; namely claims for compensation by Allied proprietors expropriated in Germany, Bulgaria, or Austria-Hungary during the war, as well as the determination of the amounts due by the respective government for these expropriations (this differed markedly from the war crimes tribunals, which were entrusted to the Reichsgericht in Leipzig (Wiggenhorn, 2005)). Even awards by the MATs at times confirmed that the purpose of their establishment was ‘solely to remove the allied party from the ordinary jurisdiction of the German courts’ (‘uniquement pour soustraire la partie alliée à la juridiction ordinaire des tribunaux allemands’ [translation by the author]) (Romanian-German MAT 1925, cited in Isidro and Hess, 2019, 242). Furthermore, national Allied courts would not have been the appropriate fora for such claims against the Central Power governments, as this would have run counter to the principle of international law that no sovereign state was to stand before foreign courts (State Immunity). Thus, the solution to refer private claims against Germany resulting from the war to arbitration tribunals, seemed to contemporaries ‘self-evident’ (Isay, 1923, 147); in particular since Germany had forced upon Russia a similar institution in August 1918 (Schätzel, 1930, 380). In addition, there were recent predecessors of international institutions that (in theory) granted individuals standing, allowing them to make claims against States, like Article 4 Convention Relative to the Establishment of an International Prize Court (1907) on the International Prize Court, or a Central American court (1907–17) that heard ten cases but declared them all inadmissible or unfounded (Baetens, 2019, 211). It seems therefore comprehensible when contemporaries insisted that the ‘innovative’ and ‘most radical characteristic’ of the MATs (compared to previous international tribunals) was ‘that not only States but also private individuals may appear before them as parties. No example of this has existed before’ (de Auer, 1927, xvii; see Hess, 2018, para 89).

10  Article 304 (a) TV stipulated that ‘[w]ithin three months from the date of the coming into force of the present Treaty, a Mixed Arbitral Tribunal shall be established between each of the Allied and Associated Powers on the one hand and Germany on the other hand’. Until April 10, 1920, 27 MATs would have had to be established by Germany and each of its former enemies. However, not all governments insisted on the MAT, but negotiated other modalities of settling private claims with Germany. Only eleven governments established MATs with Germany, in chronological order: France, Greece, Belgium, Japan, United Kingdom, Siam, Yugoslavia, Poland, Czechoslovakia, Italy, Romania (for the MAT with Portugal arbitrators were appointed, but no proceedings ever commenced, Göppert, 1931, 1; see sec D.1(c) below).

11  Given similar provisions in the other peace treaties, altogether around 100 MATs would have had to be set-up between the signatories. According to Schätzel (1930, at 389) 36 MATs were established between Allied and Central Power governments; but recent research has identified 39 MATs (Erpelding, 2022, n 17):

• •  Austria (Art 256 TSG) established eight MATs with Belgium, France, Greece, Italy, Japan, Yugoslavia, Romania, and the United Kingdom.

• •  Hungary (Art 239 TT) established eight MATs with Belgium, France, Italy, Yugoslavia, Romania, Greece, Czechoslovakia, and the United Kingdom.

• •  Bulgaria (Article 187 TN) established six MATs with Belgium, France, Greece, Yugoslavia, Italy, and the United Kingdom.

• •  In 1923 Turkey established six Mixed Arbitral Tribunals according to Articles 92 and 93 of the Treaty of Lausanne (24 July 1923) with Belgium, France, Greece, Italy, Romania, and the United Kingdom. It was an unmistakable concession that these MATs had their seat in Constantinople/Istanbul (Boeg, 1937).

• •  In addition, a Franco-Greek MAT and an Anglo-Greek MAT were established.

12  According to the Paris peace treaties, the place of each of the MATs was to be determined by the president of each tribunal (eg Art 304 TV Annex para 9). The German government assumed that the seats of the MATs would be outside Germany. The French government made clear that it expected the Franco-German MAT to be located in Paris. The Francophone Polish-German MAT, Romanian-German MAT, Greek-German MAT, and the Siamese-German MAT also had their seat in Paris, at the Hôtel Matignon, the former Austrian embassy sold by Austria and Hungary to the French State in 1920. The seat of the Anglo-German MAT and the Japanese-German MAT was in London. Rome was the seat of the Italo-German MAT. The seat of the Belgo-German MAT was first in Paris and later in Brussels. Geneva was the seat for the Yugoslavian-German MAT as well as for the one with Czechoslovakia. At times, individual sessions of MATs could be organized elsewhere, in particular at the place of domicile of the MAT president (Teyssaire and Solere, 1931).

13  In the early 1920s, the German government and in particular the German personnel of the MATs were concerned about alleged or evident anti-German disposition in the capitals of the former enemies. They feared that this inimical ‘atmosphere’, taken together with the—as they saw it—one-sidedness of the treaty’s provisions, would negatively affect the objectivity and neutrality of the arbitrators during the proceedings and their award, favouring Allied nationals (Isay, 1923, 424).

14  Article 304 (a) TV stipulated that ‘[e]ach [MAT] shall consist of three members. Each of the Governments concerned shall appoint one of these members. The President shall be chosen by agreement between the two Governments concerned.’ According to Article 304 (e) TV each government paid the remuneration of the member of the MAT it appointed and shared the costs of the remuneration of the MAT president(s). The treaties neither stipulated details about the qualification of the MAT members nor from where they should hail. It was, however, a political decision taken for granted that (i) both governments would always ‘chose [their MAT president(s)] by agreement’ among legal professionals from a State that had stayed neutral during the war, and that (ii) each government appointed one lawyer from among its nationals as MAT arbitrators. The treaties did not demand that both parties had to agree to each other’s appointees, nor did they stipulate a right to reject the other party’s arbitrator (Appointment of Arbitrators).

15  Moreover, according to Article 304 (c) TV ‘additional members’ could be appointed for each MAT and ‘each [MAT] shall sit in division’ if the high number of cases should ‘justif[y] it’. Article 304 (a) TV stipulated that each MAT section be composed of three members. France, for example, announced the creation of four divisions, called also ‘sections’ (German: Kammer) of the Franco-German MAT: Alsace-Lorraine, clearing cases, liquidation, other cases (Gidel and Barrault, 1921, 330). Until 1925, the Anglo-German MAT sat in three divisions.

16  The professional requirements for MAT presidents were demanding. Apart from being fluent in French and/or English (see sec E.1(e) below), the presidents had to excel not only in public and private international law, but also in several national private laws, particularly trade law, patent law, contracts, and intellectual property. In order to find at least four MAT Presidents for the envisioned four sections of the Franco-German MAT, in early 1920 French and German diplomats contacted several judges, lawyers, law professors, and other legal professionals from neutral countries. In 1921, Professor André Mercier of Geneva (Switzerland), Privy Counsellor Sjöborg in Stockholm (Sweden), Advocate Carel D Asser in The Hague (Netherlands), and Advocate C Botella (Spain) were appointed as presidents of the four sections of the Franco–German MAT. Altogether 17 MAT presidents presided over MATs between Germany and its former enemies: nine Swiss nationals, three Dutch, three Swedes, one Norwegian, and one Spaniard.

17  On several occasions presidents of one MAT held simultaneous double appointments in another or several other MAT(s). For example, the former president of Mexico and member of the Permanent Court of Arbitration (PCA), Francisco de la Barra, was appointed president of the Franco-Austrian and the Franco-Bulgarian MAT. The president (Baron DW Heeckeren) and the British member of the Anglo-German MAT (Heber L Hart) also sat in these capacities on the Anglo-Austrian, Anglo-Bulgarian, and Anglo-Hungarian MATs. This resulted in complaints being made about too little progress with regard to the case load.

18  If the governments could not agree on a president of the MAT, the Supreme Council of the League of Nations was to appoint a president, choosing from nationals of formerly neutral states. This was the case in 1923 during the Ruhr Crisis with the Franco-German MAT, and again in 1927 when the Polish and German governments could not agree on the successor of Professor Robert Guex of Lausanne as President of the Polish-German MAT.

19  The professional requirements for MAT arbitrators were similar to those for MAT presidents. Governments chose them from among their elite-lawyers (high-court judges, law professors, ministerial counsellors, attorneys). The appointment was considered an honour. The MATs decided by a majority of two. Assuming that the ‘national’ arbitrators would conversely decide according to what they judged best for their respective nationals or their own government’s budget, this meant that the president always had to cast the decisive vote. Contemporary observers argued that it had been a mistake in the composition of the MATs to divert from the rules set up in 1907 for the Hague PCA. The latter was composed of three neutral and two national arbitrators. The MATs, however, had only one neutral arbitrator (the president) who shouldered the entire responsibility to decide either for the State party or the private claimant (Göppert, 1931, 17). The legal disputes were thus not only fought out during the hearings with the parties, but also afterwards during the meetings of the three MAT-members. Out of frustration over their disputes with the other arbitrators, several MAT presidents resigned. However, yet it is to be underlined that also outside the frame of the MAT for reasons of costs and ease of administration most arbitrations in the interwar period provided for three-member arbitral tribunals (Carlston, 1953, 209).

20  Governments did not hesitate to recall MAT arbitrators they had appointed if they were deemed unable to adequately defend the national interest. One German arbitrator—a high ranking judge claiming his irremovability as a public servant (Beamter)—who challenged his dismissal from two MATs was told by the German Supreme Court: ‘there is no generally accepted norm in international law that members of international tribunals are irremovable’—except if this was explicitly agreed between the parties in the treaty on which the arbitration was based (RGZ 111, 115, 118). Commenting on this decision from a constitutionalist perspective, Schmitt (1926, at 364) criticized the claimant: ‘[n]o one will draw the fantastic conclusion that the plaintiff was consequently employed as a judge in a Mixed Arbitral Tribunal for life (‘Den phantastischen Schluß, daß der Kl[äger] als Richter eines Gemischten Schiedsgerichtshofes infolgedessen auf Lebenszeit angestellt sei, wird wohl niemand ziehen’ [translation by the author]). From 1920 to 1931, the Franco-German MAT alone had nine German arbitrators.

21  Each government had to appoint an ‘agent’ at each MAT who was charged with representing his country in the clearing procedures (Ausgleichsverfahren) and who oversaw the counsellors and lawyers of his nationals (Art 296 Annex para 18). If two national clearing offices disagreed, the agent initiated on behalf of his national clearing office the proceedings before the MAT. The agent was also entitled to assist and represent the creditors and debtors of his country (this was relevant especially for individuals from the former Central Powers, who were often linguistically unable to mandate on their own attorneys in Paris, London, Rome, or Geneva) or to assign attorneys to them. The government agents employed in the MAT were thus ‘a special class of advocates’ (Hart, 1932, 19), who had a ‘dominating position’ in the procedure (Isay, 1923, 419). Having the right to intervene in the proceedings, they in fact participated in all sessions and all cases before the MAT (Art 85 Franco-German MAT Rules of Procedure [‘RoP’]; but the agent could also settle claims directly with his counterpart) and processed the mass of individual claims, developing a kind of filtering system for contract and other claims and thereby prevented the MATs to being overwhelmed by the masses of individual claims. To preserve the rights of their State, agents could use their right to intervene in the proceedings even to contradict the legal or factual argumentation of their nationals (Gidel and Barrault, 1921, 331; Schätzel, 1930, 400).

22  As one former member of the Anglo-German MAT argued about the agents: ‘[t]o their conscientious zeal and conspicuous ability the efficient working of the [MAT] was largely due’ (Hart, 1932, 19). The French government defined its understanding of the role of the agent as someone who was considered not as a lawyer for private interests of those claiming damages, but who, in the public interest, was meant to urge the parties to compromise and avoid excessive demands. The agent did not act independently but received orders from his government. The first agent appointed was the French councillor Pierre J Jaudon. As chef du service des séquestres du Ministère de la Justice he was well versed in the details of the TV, which he had himself helped to draft. Based on a domestic law on the MAT (Gesetz zur Ausführung der Bestimmungen des Friedensvertrags über gemischte Schiedsgerichtshöfe und die Vollstreckung ausländischer Urteile, 10 August 1920) in Germany the national MAT agents also had an official position within the German court system. Pursuant to the obligation of Article 304 (f) TV—stipulating that national courts and authorities ‘shall render to the [MATs] direct all the assistance in their power’— German courts were obliged to give MAT agents judicial assistance (Rechtshilfe) as the German Supreme Court confirmed in 1923 (RGZ 106, 417).

23  Allied agents focused their efforts on supporting their own nationals and their advocates in their claims against the German, Austrian, Hungarian, or Bulgarian government. On the other hand, in almost all cases (except before the Polish-German MAT) the agents of the former Central Powers ‘defended’ the German government against these claims in the written part and during the pleadings of the claims before the MAT-members. This participation of the agent clearly distinguished the MATs from private arbitration (Isidro and Hess, 2019, 252).

24  The MATs comprised secretariats at the seat of each MAT, headed by secretary-generals, often distinguished lawyers. It was for the MATs to organize their personnel locally and with the support of the government agents in order to ensure the proper functioning of the tribunal and its registry. In most cases each government appointed one lawyer as the national secretary for each MAT (secrétaires-greffiers) who were then sent to Paris, London, or Rome (Art 304 Annex para 5 TV), for example Paul Fauchille for the Franco-German MAT. Also, among the officers and clerks of the MAT secretariats were a number of nationals from the Central Powers appointed by the government agents. The costs for the MAT secretariats were shared and each government paid for the personnel it appointed (Art 304 (e) TV; see the overview in Gidel and Barrault, 1921, 335).

25  The MATs were but one of several institutions set-up in accordance with the Paris peace treaties in order to execute their provisions. Other bodies like ‘clearing offices’, ‘commissariats’ etc were created and national laws enacted to regulate their work. In Germany a special ministry, the Ministry of Reconstruction (1919–24), was even set up to administer and implement the reparations regime set up by the TV. Though it was being grinded down in inter-ministerial jealousy between the Ministries of Finance, Economy, and the Foreign Office (Hainbuch, 2016), its officials assembled and provided many of the documents used by the German MAT agents during the arbitration procedure.

26  In the national capitals the MATs were administered at ministerial level, mostly by the Foreign Offices or the Ministries of Justice—which also appointed their MAT-members and the government agents (RGZ 111, 115, 118). Ministerial councillors were tasked with finding personnel for the MATs. With the help of local administrations, Allied ministerial councillors called upon the population to file their claims against the governments of the Central Powers. They were also charged with administering through subbranches the sequestration of ‘enemy property’ and the assessment of its value. As already mentioned, the French agent général for the MATs, Jaudon, was also chef du service des séquestres du Ministère de la Justice.

27  In Germany, the legal department of the Foreign Office administered the participation in the MATs. Given the growing workload of eleven MATs, a MAT-department, the ‘Commissariat for the MATs’ was set-up in 1923. In 1924–25, when the work of the MATs reached its climax, the ‘Commissioner for the MATs’ Otto Göppert (1931, 34) oversaw a total of 304 officials, 79 of them qualified lawyers. Subdivided in four groups, most of them performed their duties in Berlin, while some were sent to the German MAT agent’s offices in Paris (seven lawyers and seven clerks), London (five lawyers and four clerks), and Rome (two lawyers and three clerks).

28  For the Franco-German and the Polish-German MATs, it was formally agreed that all members of the tribunals and the personnel of the secretariat should profit from diplomatic immunity and privileges (Immunity, Diplomatic). Also in Great Britain, the German members of the MAT were recognized as ‘exterritorial’ (Schätzel, 1930, 401) (Privileges and Immunities of International Courts and Tribunals).

29  For the claimants, representation by attorney was ‘purely permissive’ according to the MATs’ rules of procedure (United Nations (‘UN’) Law Commission, 1955, 41), although it was the rule in major cases; in cases considered of less importance, parties were represented by their government agents (Isidro and Hess, 2018, 252). Anyone qualified to practice law in his (all legal professionals involved in the MATs were men) country could represent a claimant before the MAT (Hart, 1932, 19); this also included law professors. Thus, German defendants or claimants could task a German attorney with representing their interests before the MAT in Paris, London, Geneva, or Rome. However, due to the high costs for the travel and daily rates this was rarely the case. Moreover, there were few attorneys among Central Power nationals who could plead in French, English, or Italian (see sec E.1(e) below). Therefore, German or Austrian individuals repeatedly hired English and French attorneys to represent their interests before the MAT. In the early 1920s this resulted in ‘fierce denunciations’ by the French press of these French nationals, depicting them as ‘traitors’ (Göppert, 1931, 13). Similarly, the German government hired external legal support for the most important cases. Besides the government agents, law professors Erich Kaufmann and Josef Partsch, as well as Berlin attorney Ernst Wolff and several English and one French attorney pleaded for Germany before the Franco-German and the Anglo-German MATs.

30  The growing number of cases that had reached German ministerial desks through the MAT secretariats since 1920 found the German legal profession unprepared. It proved challenging to find German lawyers able to understand and successfully work with the long articles of the TV written in the most technical French and English legal language. However, the German difficulties to win cases before the MAT ran deeper than mere matters of language proficiency. The German arbitrators, MAT agents, and scholars were slow to appreciate that it was ‘insufficient’ to consider the treaty ‘with the eyes of a German lawyer’ (Isay, 1923, iii), because the Treaty’s terminology was based on distinct ideas of French and English law. Thus, the ‘solution to legal questions concerning contracts, debts, property rights, unfair competition, shipping, intellectual property, judgment, prescription, and social insurance had to be found in French and English legal concepts (such as dette), interpretation methods, and legal institutions and traditions (for instance, tribunal, court)’ (Clark, 2001, 42). Resultingly, early German attempts to win MAT-cases proved ‘practically inadequate’ (Clark, 2001, 42).

31  The Commissariat of the MATs had to realise that ‘the German party was lost if it could not follow … [the English and French] interpretation’ of the Treaty’s provisions and, similar to German legal scholars, recognized this as a ‘crisis of comparative law’ (Nörr, 1988, 102). In part, these problems were intrinsic to German legal education—namely the neglect of comparative law perspectives and the lack of teaching of foreign law. Considering the sudden ‘practical relevance’ of both (Makarov, 1947, 360), the Commissariat of the MAT subsequently sought not only academic support, but also attempted to instigate increased academic research into the MATs. Law professor Joseph Partsch of Berlin University was appointed head of the Commissariat’s own ‘academic department’ that not only gave advice in specific cases, but also published academic articles about the MAT and individual decisions in German and French (Göppert, 1931, 29).

32  Moreover, in 1924, also with support from the Reich Ministry of Justice and other institutions, Viktor Bruns, previously a law professor in Geneva who spoke fluent French, founded the Kaiser Wilhelm Institute of International Law and Foreign Public Law in Berlin. Two years later, under the leadership of Ernst Rabel, a Kaiser Wilhelm Institute for Foreign and International Private Law was established in Berlin. Throughout the 1920s, both Institutes owed much of their existence and continued governmental support to the fact that their members were repeatedly called upon by the Foreign Office for support in all matters related to the MATs. Both Bruns and Rabel took over direct responsibility in the German MAT proceedings, Rabel as arbitrator in the Italian-German MAT, Bruns in 1927 as arbitrator in the Polish-German MAT.

33  The research undertaken by the German scholars working in these institutions was unmistakably influenced by the notion of a peace treaty system that was considered to have been forced upon Germany and its allies to the detriment of justice and fairness in international relations. The published texts barely claimed academic disinterestedness, but constantly pitted ‘us’ against ‘them’, complaining about the one-sided MATs as ‘tools’ for the victors (eg Schätzel, 1930, 380) based on a ‘decrepit’ legal order, the ‘evil spirited’ TV (Mendelssohn Bartholdy, 1922, 33; 45).

34  The competences of the MATs to decide disputes regarding private rights affected by the war were stipulated in sections III–VII of Part X TV. For reasons of an overview, the following classes of cases will be distinguished (Heilberg, 1919, 121; Witenberg 1925; Blühdorn 1932):

1. (i)  ‘Debts’ according to Section III (Art 296)

   The MATs were competent to decide on disputes between the national Clearing Offices (Ausgleichsämter) about the payments of outstanding pre-war debts/credits. Additionally, they had to decide if the parties appealed against joint awards of both Clearing Offices (Annex Art 298 paras 16 to 21 TV).

2. (ii)  ‘Property, rights and interests’ according to Section IV (Arts 297, 298 TV)

   (a) The MAT were to determine the total amount of compensation to be paid by Germany to the Allied nationals for damage or injuries inflicted upon their property, rights or interests in German territory as it existed on 1 August 1914, as a result of the application of so-called German exceptional war measures (Art 297 (e) TV); (b) MATs also decided on claims by former Central Power nationals against the newly formed States due to the liquidation of their property resulting in particularly low prices (Art 297 (h) (2) TV); (c) MATs were also entitled to appoint arbitrators if other persons requested were unwilling or unable to do so (eg Annex Art 298 (4) TV).

3. (iii)  ‘Contracts, Prescriptions, Judgements’ according to Section V (Arts 299–303 TV)

   (a) The MATs were to grant ‘equitable compensation’ to a prejudiced party if an Allied national had to execute a contract with a (former) enemy ‘in the general interest’, as defined by Allied governments (Art 299 (b) TV); (b) the MATs were to grant compensation to the prejudiced party if the restoration of the rights of an Allied national who was prejudiced by measures of execution in Germany were ‘inequitable or impossible’ (Art 300 (b)–(c) TV); (c) if a prejudiced party to a contract between enemies that had been dissolved due to the failure of either party could apply to the MAT for relief (Art 300 (d) TV); (d) if a judgment by a German court, also in occupied territories, had prejudiced an Allied national, s/he was entitled to compensation to be fixed by the MAT (Art 302 TV); (e) the MATs were to appoint an actuary who determined the assets to be handed over from a German insurance company to an Allied government if the latter wished to cancel insurance contracts between the German company and its nationals (Annex to Art 303 (12) TV).

4. (iv)  ‘Mixed Arbitral Tribunals’ according to Section VI (Art 304 (b) TV)

   (a) The MATs had to decide ‘all questions … relating to contracts concluded before the coming into force of the present Treaty between nationals of the Allied … Powers and German nationals’, except where these questions fell under the jurisdiction of the national courts of the Allies; (b) when a national court decided on a question covered by Sections III, IV, V, or VII, but ‘inconsistent’ with these provisions, the prejudiced party was entitled to obtain redress by referring the matter to the MAT (Art 305 TV). Thus, in these cases the MATs ‘acted functionally as a kind of second instance court’ (Isidro and Hess, 2019, 244; see Marx, 1924, 597).

5. (v)  ‘Industrial, literary or artistic property’ according to Section VII (Art 310 TV)

   The MAT had to fix the conditions to grant a new license from the German proprietor of intellectual property rights, and if necessary, fix the amount to be paid for the use of such rights during the war.

35  It is to be emphasized that throughout their existence, the competence of the MATs remained a highly disputed field of legal reasoning—before the tribunals and among international law scholars. Germans tended to read the provisions of the TV as narrowly as possible, whereas their adversaries in the MATs argued to the contrary. In a much-debated award of the Franco-German MAT (Fourth Section, Société Vinicole v Mumm, 4 March 1921) the tribunal stated: ‘it is clear that the treaty [of Versailles] intended to make the competence of the [MATs] as wide as possible’ (translation in Strupp, 1923, 663).

36  The ‘one-sidedness’ and ‘unilateralism’ (favouring Allied nationals) found in the general MATs’ competencies (Isidro and Hess, 2019, 245 et seq) were mitigated by the jurisdiction of MATs between the states of the former Central Powers and the ‘new States’ in east central Europe (Poland, Czechoslovakia, and Yugoslavia). These MATs, and additional special agreements between these parties, offered redress for nationals of the former Central Powers who had lost their property due to ‘liquidations effected in new States’ after 1918 in case the ‘sale or measures taken by the Government of the [new] State [eg the Polish Republic] … were unfairly prejudicial to the price obtained’ (Art 297 (h) (2) TV) (comparable provisions in Art 249 (i) TSG; Art 232 (i) TT; Art 177 (i) TN).

37  The possibilities of legal protection against, for example, Polish or Czechoslovak liquidations of German, Austrian, or Hungarian property were considerable and clearly speak against a general ‘lack of reciprocity’ of the MATs, which was deplored by German authors (Strupp, 1923, 664). The Polish-German MAT even saw cases where ethnic Germans who had become Polish citizens in accordance with the TV claimed compensation from Poland, ie their own government.

38  Art 92 TV (referring to Article 297 (h) (2)) on the liquidation of ‘the property, rights, and interests of German nationals’ in ‘German territory transferred in accordance with the present Treaty and recognised as forming definitively part of Poland’ required the plaintiff to prove his or her prejudice before the MAT; for example, the sale price of an estate below market value or if the seller, the Polish authorities, were alleged to have based the item for sale on an incorrect value (eg złoty instead of mark) (Kaufmann, 1922, 10, 67).

39  As stated above (in item (iv) in sec D.1(a)), Article 305 TV gave a general competence to each MAT to revise domestic court decisions ‘inconsistent’ with sections III, IV, V, or VI TV (Mendelsohn-BArtholdy, 1922, 38). This ‘extraordinarily wide range of the paramount authority’ of the MATs (Hart, 1931, 392), thus offered a remedy that was also open to nationals of the former Central Powers affected by Polish, Yugoslav, or Czechoslovak court decisions about the liquidation of and compensation payments for their property.

40  Several States and their nationals around the world had suffered damage from German war measures despite the fact that these States were, at the moment the damage occurred, not yet at war with Germany, but neutral. The affected governments, most of all the United States (‘US’)—having lost several vessels sunk by German U-boats before it declared war on Germany in 1917—insisted on the compensation of these ‘neutrality-damages’. According to paragraph 4 of the Annex to Articles 297–98 (hereinafter ‘paragraph 4’):

Provisions similar to paragraph 4 were included in the Treaties of Saint-Germain-en-Laye, Trianon, and Berlin. This so-called Lusitania-clause (named after the British ocean liner Lusitania, sunk by German U-boat on 7 May 1915, killing many US nationals) formed the basis of claims laid against Germany by the governments and nationals of Greece, Portugal, and—later in its version of the Treaty of Berlin (1922)—the US (Isay, 1923, 198).

41  Paragraph 4 did not refer claimants to a MAT for an assessment of their claims, but to a single arbitrator. It was thus called the MAT’s ‘little brother’ that had to decide about similar matters of fact before the official declaration of war (Schätzel, 1930, 388). It did not stipulate the arbitrator’s nationality or ‘neutrality’. But the fact that the Swiss Federal President, Gustave Ador, was named to appoint the arbitrator indicates that the framers of this provision assumed that Ador would appoint either one of his nationals or a citizen of another neutral state, thereby avoiding the potential characterization of paragraph 4 as a tool of ‘victor’s justice’. Paragraph 4 also left other questions open. Nor did it stipulate a particular place of trial or who should determine the place. Also, paragraph 4 did not state who should request Ador to appoint an arbitrator or anything about his qualifications, but it was apparently self-evident that only a person with legal training would be qualified for this task.

42  Though it was disputed who could raise claims for neutrality-damages, in practice according to paragraph 4 these claims were open to the Governments whose neutrality had been violated by an act committed against one of their nationals. In accordance with general principles of law, claimants under this article were only entitled to damages which arose directly out of the alleged violation of (inter-)national law and were causally connected to it. Furthermore, only damage to property, rights, and interests and no damage caused to individuals could be claimed under paragraph 4.

43  The inclusion of an arbitrator in the Lusitania-clause was one of the few negotiation successes of the German delegation in May 1919. After the Germans had received the draft treaty text, they were given 14 days to respond. Most of the German proposals were rejected in the Allied response of 16 June. However, the Allies agreed to organize a plebiscite on the future of Upper Silesia. And they conceded to the German request to have all Allied ‘neutrality claims’ assessed by an arbitrator, thus giving up government control over the amounts to an independent lawyer (Zollmann, 2016, 255–61).

44  Questions about the law to be applied in the MATs were constantly debated throughout the existence of MATs as there ‘was almost no explicit provision’ in the peace treaties (Isidro and Hess, 2019, 269; see Goldschmidt, 1945, 100).

45  The peace treaties contained provisions that served as a substantive basis for claims for compensation against the former Central Powers. Articles 297 (e) TV, 249 (e) TSG, 232 (e) TT, and 177 (e) TN entitled Allied and Associated nationals to ‘compensation in respect of damage or injury inflicted upon their property, rights or interests … in German [or Austrian] territory as it existed on August 1, 1914, by the application either of the exceptional war measures or measures of transfer’. Thus, it did not matter for the MAT if these ‘exceptional war measures’ had been executed in accordance with the domestic special war-laws of the Central Powers. Schätzel (1930, at 419) argued that even requisitions by the Central Powers in accordance with the Convention respecting the Laws and Customs of War on Land (1907) meant that the Allied nationals were entitled to compensation according to Articles 297 (e) TV, etc.

46  In those cases, however, where treaty provisions merely mentioned that the MATs were competent, without stipulating the law to be applied to the facts, MAT-members resorted to the same solution as domestic courts would have done. They determined in each individual case, for example, the execution of a pre-war contract between Allied and Central Power nationals, what national law should be applied according to the existing rules of private international law, and the conflict of law rules (Ophüls, 1962, 174). For this reason, the composition of the MAT proved advantageous as always at least one of the MAT members was familiar with the (at times conflicting) national laws in question.

47  However, also in cases where domestic laws would have applied, individual peace treaty provisions could overrule their application. For example, in the ‘legally most difficult part of the peace treaty’ (Nussbaum, 1922, 1) Article 296 (4) (d) TV required the payment of debts ‘in the currency of such one of the Allied and Associated Powers’, no matter what the parties had previously agreed on about the payment. Article 299 (a) TV made explicit that (international) private law agreements were subservient to the provisions of this international treaty:

48  Since the treaty text decided if and which classes of contracts ‘between enemies’ were exempted from the general rule of dissolution (‘in the general interest’ (Art 299 (b) Annexes); for example, fire insurance, life insurance; Drost, 1948, 93; Wolff, 1921), the distinction between domestic, private, and public international law was less clear than ever, as not only practitioners of international law noted. With a view on contemporary developments towards an ‘international judicature’, Kelsen (2008 [1934], 143) recognized ‘the tendency to blur the line between international law and national legal order’ (‘die Tendenz, die Grenzlinie zwischen Völkerrecht und einzelstaatlicher Rechtsordnung zu verwischen’ [translation by the author]). Given this ambiguity Makowski (1931, at 298) went so far as to argue that the MATs were not ‘organes internationaux’, but joint institutions of the two participating States that also apply ‘national laws’.

49  Isay (1923, at 427) spoke of ‘international private law as part of public international law’. Indeed, the peace treaties ‘contained many provisions that were of purely private law nature’, and also public law provisions of the treaties had ‘massive consequences’ in private law relations. Another challenge was the seeming intention of the TV to regulate ‘uniformly’, ie with the ‘same expressions and provisions, the legal relations in not less than 24 jurisdictions that are … different in their norms, legal institutions, and legal expressions’ (Heilberg, 1919, 3–4). Given these challenges, Isidro and Hess (2019, 272) find that the MATs did not a develop a ‘common approach’ to a uniform applicability of law(s). The MAT members solved disputes ‘pragmatically’ ‘on a case by case basis’, knowing that the MATs were neither bound by their own previous decisions nor by other MATs.

50  Since MATs were tribunals with a ‘juridiction internationale’ created under international treaty law (Gidel and Barrault, 1921, 325)—which resorted, on a case-by-case basis, to private international law and to national laws—they also fell back on general principles of public international law and ‘(assumed) general principles of law: [like] respect for vested rights’ (Isidro and Hess, 2019, 273) (General Principles of Law). Discussing procedural questions on interim judgments, the Polish-German MAT, for example, explicitly applied ‘a rule enshrined in the generality of continental laws’ (‘une règle consacrée par la généralité des droits continentaux’ [translation by the author]) (quoted in Schätzel, 1930, 412). The facts underlying cases before the MATs involved public international law questions concerning State succession (Alsace-Lorraine, the ‘new States’), nationality, treaty interpretation, or governmental liability. Yet in retrospect, Jessup (1956, at 95) argued that ‘[s]ince the cases [decided by the MAT] were not international in the sense of being State v State, public international law, or what the Permanent Court called true international law, was not considered generally applicable except for the purpose of interpreting the [peace] treaties’. However, the wording of individual provisions also required the application of norms of public international law. A case in point was paragraph 4 of the Annex to Articles 297–98 TV on the neutrality damages ‘growing out of acts committed by the German Government … since July 31, 1914, and before that Allied or Associated Power entered into the war’. The provision that the claims must grow out of ‘acts committed’ made it evident that the arbitrator would have to establish factually that the ‘acts’ in question bore the features of a delinquency and must thus be acts violating an existing domestic or international norm like the Hague Conventions (Zollmann, 2016, 260). In light of such requirements, Bruns (1929, at 1) lamented that contemporary arbitration tribunals, including the MATs, had, however, based their awards on norms ‘that formed neither part of treaty law, nor of recognized customary law’. Criticizing the argumentation in a number of arbitration awards, Bruns posed the pertinent question regarding how arbitrators establish the legal norms they apply in their awards; ‘[o]r are these norms not part of positive international law?’ (1929, at 1)—implying thus that (politically motivated) considerations of equity had found their way into individual (MAT) awards. Strupp, too (1930, at 45 and 76), pleaded for a restrictive interpretation of equity by ‘international judges’, urging them to adhere to established norms of public international law as the basis of their awards (Equity in International Law).

51  The MAT procedure to be followed was not defined in the respective peace treaties. Rather they stipulated that each MAT will ‘adopt such rules of procedure as shall be in accordance with justice and equity’ (Art 304 TV Annex para 2). The resulting ‘wreath of small rules of procedure’ of each MAT (RoPs, Mendelssohn Bartholdy, 1922, 39) were so detailed that contemporaries described them as ‘miniature civil procedure codes’ (Calamandrei, 1922, 305; translation in Requejo Isidro and Hess, 2019, 253). The MAT rules of procedures were considered to be the first rules that dealt with mass claims on an international level.

52  International procedural law had barely been systematized before the First World War, even though there had been attempts since the late 19th century (International Courts and Tribunals, Procedure). Yet, Rosenne (1963, at 18) claimed that ‘[b]y the outbreak of the First World War, the main lines of international arbitral procedure were firmly drawn’, namely five ‘essential features’: (i) disputes about the tribunal’s jurisdiction should be settled by the tribunal and ‘not be referred back to diplomatic channels’; (ii) arbitrators should be ‘persons of recognized competence’ and integrity; (iii) parties ‘accepted elements of normal judicial techniques’, such as the equality of the parties and independence of the arbitrators; (iv) ‘regular patterns of procedure began to establish themselves’, including written and oral pleadings, ‘closed deliberation’ of the arbitrators, promulgation of the arbitral award, and the duty of arbitrators to give reasons for their award; (v) the political will to consent to arbitration ‘contained the obligation’ to accept the award as final and binding and to ‘carry it out in good faith’ (General Principles of International Procedural Law).

53  Broadly speaking, these principles were recognized in all rules of procedures the MATs adopted according to Article 304 TV Annex paragraph 2. In particular they made explicit the principle that ‘it is inherent in the arbitral (and judicial) process that a tribunal is the judge of its own jurisdiction, that it has compétence de la compétence’ (Schwebel, Sobota, and Manton, 2020, 3; see Art 87 Franco-German MAT RoP; Art 3 Belgo-German MAT RoP; Art 3 Polish-German MAT RoP; Isay, 1923, 430; Lauterpacht, 2004 [1928], 402; UN Law Commission, 1955, 45–47) (Competence-Competence).

54  The presidents of the MATs met to determine the general features of the rules of procedure and to supervise the proper functioning of the entire MAT jurisdiction (collège des présidents, Gidel and Barrault, 1921, 331). Between 1920 and 1923, most MATs formulated their rules of procedure. The Franco-German MAT RoP of 2 April 1920 was the first to be published (in the Journal Officiel) and applied. Also, the German government published all RoPs of the MATs in which Germany participated in the government gazette and its annexes (since 1922, Reichsgesetzblatt Teil II; overview in Isay, 1923, 428). If both governments agreed, the RoPs were over the course of the MAT-works supplemented and republished.

55  Carlston lamented ‘an age-old problem in international arbitration of bringing tribunals to a realization of the importance of procedural rules and ensuring respect for their impartial and inexorable application’ (1953, at 206). Contemporary observers of the MATs also noted that the MAT members did not always adhere to a uniform application of the RoP, but used the provision so that they could stray from the rules (see Schätzel, 1930, 403, 411; Art 99 Franco-German MAT RoP, or Rule 45 Anglo-German MAT, RoP, 4 September 1920: ‘[t]he Tribunal will … grant other dispensations from these rules in all such cases as may be necessary in the interest of justice and equity’). Contemporary scholars distinguished two ‘types’ of MAT RoPs: the ‘Franco-German MAT type’ and the ‘Anglo-German MAT type’ from which most other MATs more or less ‘replicated’ (Isay, 1923, 428; Mendelssohn Bartholdy, 1922, 40). Both ‘types’ were visibly influenced by the French or English rules of procedure. The treaty text explicitly authorized the parties to the dispute ‘to present orally and in writing to the [MA] Tribunal arguments in support or in defence of each case’ (Art 304 TV Annex para 3). Thus, the proceedings in both ‘types’ were organized in two stages, a written part and an oral part. The RoP determined the period within which an action/claim must be brought before the MAT (the secretariat, Arts 3 and 6 Franco-German MAT RoP), though—for reasons of equity—exceptions were permitted (Art 98 Franco-German MAT RoP; Rule 45 Anglo-German MAT RoP). During the written stage, the parties had to present the MAT members with all the facts they deemed relevant; later submissions were only exceptionally permitted. Years could pass between both stages of the proceedings.

56  According to the French-‘type’ RoP, four memoranda had to be submitted to the MAT (six copies each) within a prescribed period: the claim, strictly enumerating all ‘facts’ followed by a statement of law; after two months the réponse/statement of defense (Art 13); after one month the réplique/reply (Art 26); and after another month the duplique/rejoinder (Art 28). Subsequently the oral proceedings commenced with the representatives of the parties and in which the government agents had ‘the last word always’ (‘toujours la parole les derniers’ [translation by the author]) (Gidel and Barrault, 1921, 332). The MAT members were allowed to hear witnesses before they rendered their award.

57  The English-‘type’ RoP required the parties to submit four memoranda on questions of law and facts—whereas the required structure of the texts, focussing on ‘the nature of the claim’ differed markedly from the French ‘type’. If the MAT members considered the submitted claim to be without merit, they could dismiss the entire action without hearing the parties. Whereas according the French-‘type’ RoP parties were—within one year following the arbitration award—allowed to appeal on points of law for facts that had become known and that would have substantively influenced the MAT-award, this was not possible in the English-‘type’ RoP.

58  Even though the MATs were given ‘[c]omplete freedom as to the evaluation of evidence submitted’ (UN Law Commission, 1955, 60; see Gidel and Barrault, 1921, 334) preferences became clear: in the French-type RoP the ‘actes et documents’ were the ‘privileged pieces of evidence’ that were to be attached to the memorandum (Mendelssohn Bartholdy, 1922, 43); whereas the hearing of witnesses was provided for in the RoP, in practice it was rather uncommon. In contrast, in the Anglo-German MAT the hearing of witnesses was the norm and, in addition, the ‘parties shall have the right themselves to give evidence and shall if required by the Tribunal do so’ (Rule 31 (a) Anglo-German MAT RoP); a cross-examination of witnesses was also possible. Given the geographical location of the seats of the MATs, it was difficult and costly, especially for the government agents of the former Central Powers and the ‘new States’, to organize the hearing of ‘their’ witnesses. In exceptional cases the MAT presidents were willing to travel to Germany or other places to examine witnesses. In addition to Article 304 (f) TV obliging the governments to order their ‘courts and authorities … to render the [MAT] … all the assistance in their power, particularly as regards transmitting notices and collecting evidence’, in paragraph 7 Annex to Art 304 TV Germany had explicitly agreed ‘to give the Tribunal all facilities and information required by it for carrying out its investigation’. Further, the RoPs authorized the tribunal to order inquiries to establish (additional) facts and to appoint experts for this purpose (Art 56 Belgo-German MAT RoP). The RoP of the Franco-German MAT also made possible a descente sur les lieux (Art 61) (Site Visit), a visit by the tribunal to the scene to which a case relates, which it rarely undertook (Schätzel, 1930, 407; Göppert, 1931, 14). If one of the parties failed to appear, the proceedings continued, as stipulated in Article 58 Italo-German MAT RoP, ‘[t]he failure of a party to appear at a hearing shall not interrupt the course of the proceedings. The tribunal may order a postponement or render a judgment on the basis of the evidence in the case.’ The MAT president held policing powers during the tribunal’s session.

59  The hearings of the MAT were generally open to the public (Public and Media Access to Courtrooms: International Courts and Tribunals). Located in prominent places in the centre of Allied capitals such as the Hôtel Matignon, the seat of several MATs in Paris, these hearings had regular visitors and were attended by journalists. Awards of the MAT that were considered as particularly important were collected and published in the Recueil des Décision des Tribunaux Mixtes (ten volumes) under the auspices of the French Clearing Office (Office des Biens et Intérets Privés) and France’s agent-géneral, Pierre Jaudon, (it soon became clear that not all awards could be published). This collection of published awards (only rarely containing awards by neutrality arbitrators according to paragraph 4) became a major source for legal doctrine in the 1920s and 1930s. Though most MATs delivered reasoned awards in writing to the parties, there were a few divisions within MATs that did not deliver reasoned awards, for example the second division of the Anglo-German MAT, established in 1923 (Dickson, 1923, 301).

60  The language of the MAT proceedings was (unless otherwise agreed) English, French, Italian, or Japanese (Art 304 Annex para 8), according to the Allied party. For all representatives of the former Central Powers, the arbitrators, the staff, but most of all for the government agents, it remained a major challenge that all legal memoranda and all other documents as well as the oral proceedings were to be written or presented by them in a foreign language. The French, British, Belgian, and Italian parties and their representatives, including the government’s agent, on the other hand, could write and speak in their mother tongues. The German government agent Schätzel (1930, at 405) stated it was ‘totally inappropriate’ (‘völlig unangebracht’ [translation by the author]) that French was the obligatory language for all claims related to Alsace-Lorraine, where the majority of claimants were German-speaking, forcing both parties to plead in a foreign language. The languages of the other MATs with Asian or Eastern European governments were either English or French. However, under exceptional circumstances the Polish, Czechoslovak, and Yugoslav party allowed the use of German during the proceedings and in documents (Isay, 1923, 444). Moreover, the awards of these MATs were given in French, English, or Italian. For German commentators, all these ‘language difficulties’ (Schätzel, 1930, 455) illustrated the ‘discriminatory character’ of the MAT proceedings (Isidro and Hess, 2019, 258). Especially in the early years of the MATs, the language barrier between the parties proved highly detrimental to German, Austrian, Hungarian, and Bulgarian attempts to reject claims by Allied nationals.

61  The MATs’ operating costs, including the ‘remuneration of the President’, were borne equally by the governments involved, and each government paid the expenses for the personnel ‘appointed by it’ (Art 304 (e) TV). As high-ranking officials (who had to be deputized for in their original position) and attorneys involved in the MAT procedures received attractive allowances for living abroad in addition to their salaries, the overall costs of the MAT apparatus were rather high, and Finance Ministries regularly urged downsizing the apparatus and to terminate the MAT work sooner rather than later (Zollmann, 2021, 69; Zollmann, 2016, 266).

62  Claimants had to pay the MAT fees in advance before the service of the writ—except where the government agent confirmed the claimant’s impecuniosity. Further, the MAT was ‘empowered to award the sums to be paid by the loser in respect of the costs and expenses of the proceedings’ (Art 304 (d) TV).

63  Contrary to traditional notions of diplomatic protection in international law, providing that an injury to an individual by a foreign State is (exclusively) actionable by that individual’s State, Kelsen (2008 [1934], at 143) noted an increasing ‘tendency [in international law] towards direct entitlement and obligation of individuals’ (‘Tendenz [in international law] zu unmittelbarer Berechtigung und Verpflichtung der Individuen verstärken’ [translation by the author]). For him, this ‘tendency’ was most palpable in the ‘provision of central organs for the creation and implementation of legal norms’ (‘Ausbildung von Zentralorganen zur Erzeugung und Vollziehung der Rechtsnormen’ [translation by the author]) and for both the MATs were prime examples during the 1920s and 1930s. Practically for the first time, individuals were given direct access to international arbitration bodies, the MATs, to press their claims against former enemy States. This standing of individuals having their subjective rights under (public) international law and the individual complaints procedures available to them were indeed the ‘most prominent and innovative feature’ of the MATs set up by the Paris peace treaties (Isidro and Hess, 2019, 243). Contemporaries described this ‘particularity’ of the MAT as breaking with the general principle that only States have standing before international tribunals as an ‘anomaly’ (Makowski, 1931, 298).

64  Private claimants before the MAT had to be nationals of the MAT to which they submitted their claims, and they still had to have this nationality when this MAT rendered its award—otherwise the MAT was no longer competent (Isay, 1923, 435). Considering the change of nationality by millions of individuals following the citizenship regimes set by the Paris treaty system for the ‘new States’ in Central Eastern Europe this was not always possible and claimants lost their standing before the MAT.

65  However, beginning in the late 1920s the dominating position under international law of the States having agreed on the creation of the MATs vis-à-vis their concerned nationals having claims became apparent yet again. Referring to agreements concluded following the Young-Plan (1930) that regulated the reparation regime with Germany and related property claims (Dawes Plan (1924) and Young Plan (1930)), one of the legal advisers of the British Foreign Office, WE Becket, summarized in a letter to H Lauterpacht in 1935 what can be termed as a sceptical perspective on the legal position of the individual within the system of the MATs:

The Governments who set up Mixed Arbitral Tribunals can, and in some instances have abolished them, changed their original jurisdiction, agreed that certain judgements delivered by them shall not be effective or shall be subject to appeal etc., etc. How is all this action by the Government, taken without the consent of the individual concerned, consistent with the view that the individual had legal rights in this respect?’ (cited in: Lauterpacht, 2004, 740).

The diplomat and lawyer thus underlined that the individual for all his war-related claims remained at the mercy of his government and that, irrespective of any ‘rights’, the traditional notion of ‘diplomatic protection’ could be reinstated any time.

66  The decisions of the MATs were ‘final’ and ‘binding upon [the parties’] nationals’ (Art 304 (g) TV). The enforcement of the decision was a responsibility of the governments concerned, not of the tribunal. In order to implement the direct enforceability of all MAT decisions without any exequatur procedure (Art 302 TV), Germany enacted the Law of 10 August 1920 stipulating that all MAT decisions are ‘final’ and that they have the binding force of a decision of a national court (para 3). The law conferred on the Landgericht Berlin the competence for all enforcements (Isidro and Hess, 2019, 262). If the MAT decision obliged an individual in Germany to pay a specific sum, the German government agent provided the claimant with a certified translation that was then the enforceable deed for the German bailiff. In the Anglo-German MAT, for example, in some cases orders of payment were made reaching ‘a thousand pounds or more’ (Hart, 1932, 19).

67  More pressing for the governments of the former Central Powers were claims for compensation by Allied nationals against Germany, Austria, Hungary, or Bulgaria. These governments tried their utmost to avoid cash payments, using the ‘weirdest constructions of thought’ (‘eigenartigsten Denkkonstruktionen’ [translation by the author]). They insisted that the clearing offices in the former enemy States would have to credit the awarded sums from the liquidation revenues (Liquidationserlös) of German property liquidated in the former enemy States (Schätzel, 1930, 447). As a result, Allied creditors having won an MAT award were referred by the German government to their own governments for the settlement of the creditor’s claims out of the liquidation revenues. German officials were well aware that many of such claims remained unsettled (Göppert, 1931, 22).

68  According to Article 304 (g) TV, the MATs’ awards were ‘final and conclusive’, meaning that in general there was no appeal against them (Finality of Judgments; International Courts and Tribunals, Appeals). However, within one year of the tribunal’s decision, parties could ask for a revision if new and substantive ‘facts’ became known that would have materially influenced the decision had they been known before (eg Article 79 et seq Franco-German MAT RoP). According to Schätzel (1930, at 416), parties regularly tried this means, but rarely convinced the tribunal. Yet Thieme (1927, at 4) pointed out that the mere possibility that decisions could be ‘re-examined’ increased the ‘moral power and reputation’ (‘moralische Kraft und das Ansehen’ [translation by the author]) of the MAT.

69  In other cases, parties argued that the MAT was not competent to decide the dispute and, protesting in vain that the tribunal continued its proceedings, claimed an excès de pouvoir of the MAT members. In Germany such disputes led to at least one Supreme Court case (RGZ 121, 180) that found that German courts were not competent to ‘re-examine’ an MAT award. In the famous Polish-German dispute over Poland’s liquidation of the factory at Chorzów, in Upper Silesia in a border area that since 1922 fell under Polish jurisdiction, the German company, still owners in 1922, filed a case with the Polish-German MAT demanding it to order the Polish Government to restore the factory and pay reparations. While the matter was pending before the MAT, the German government approached the Permanent Court of International Justice (PCIJ) claiming that Poland violated the Polish-–German Convention on Upper Silesia of 15 May 1922. Before the PCIJ, Germany argued that the ‘Polish Government in carrying out these liquidations [of the factory at Chorzów] has not acted in conformity with the provisions of Articles 92 and 297 of the Treaty of Versailles’ (German Interests in Polish Upper Silesia, Germany v Poland, 1925, sec 2; German Interests in Polish Upper Silesia Cases). The Polish government, in turn, argued that Germany’s suit was inadmissible as the PCIJ had no jurisdiction over this case—among other reasons because ‘this application [by Germany] cannot be entertained until the Germano-Polish Mixed Arbitral Tribunal in Paris has given judgment in the dispute regarding the same factory, which the … Company submitted to that Tribunal on November 10th, 1922’ (at sec 49). However, in 1925, the PCIJ decided that it had jurisdiction, arguing that:

it is clear that the essential elements which constitute litispendance are not present. There is no question of two identical actions: the action still pending before the Germano-Polish Mixed Arbitral Tribunal at Paris seeks the restitution to a private company of the factory of which the latter claims to have been wrongfully deprived; on the other hand, the Permanent Court of International Justice is asked to give an interpretation of certain clauses of the Geneva Convention. The Parties are not the same, and, finally, the Mixed Arbitral Tribunals and the Permanent Court of International Justice are not courts of the same character, and, a fortiori, the same might be said with regard to the Court and the Polish Civil Tribunal of Kattowitz (German Interests in Polish Upper Silesia, Germany v Poland, sec 55; see also Makowski, 1931, 298).

70  Among the most politicized of these disputes about the MAT’s competence were conflicts among Eastern European governments about the execution of their agrarian reforms and the property of ethnic minorities. As a result, the League of Nations was involved. A compromise was negotiated that the PCIJ should act as a ‘court of appeal’ regarding judgments on questions of jurisdiction or merits for a number of MAT awards based on specific agreements between the governments concerned (eg Agreement for the settlement of questions concerning agrarian reforms and mixed arbitral tribunals, between Hungary, Romania, Czechoslovakia, and Yugoslavia. Paris, 28 April 1930; see Erpelding, 2022, 11). Three years later the PCIJ rendered its first judgment (Pazman University (Hungary) v Czechoslovakia (15 December 1933); The Pajzs, Csáky, Esterházy case, Hungary v Yugoslavia, (1936)).

71  The MAT members in turn had to deliberate on questions related to the possible choice claimants had between the jurisdictions of national courts and international MATs (Art 304 (b) TV) (Forum Choice and Forum Shopping). Repeatedly, the option for the dispute to be heard before the MAT was chosen. In Rafael Cappon and Son v Vereinigte Glühlampen- und Elektrizitäts AG (1929) the Hungaro-Romanian MAT held, with reference to Article 239 (b) Treaty of Trianon, that once the claimant—as authorized by this treaty—decided to bring his claim before a domestic tribunal, he was bound by his choice and thus precluded from having recourse to the MAT (Lauterpacht, 1993, 433). Yet, the ‘saga’ of the above-mentioned Mumm case on the champagne trademark and company, sequestered by France in 1914, and the right to restrain the use of a surname continued not only be heard before the MAT (1921, 1923, 1933), but also before French (1930, 1932) and US courts (11 F Supp 208 (1935)).

72  Much to the chagrin of the former Central Power governments, Allied governments encouraged their nationals to claim compensation from former enemies and, after an initially slow start in 1920–21, individual Allied claimants came forward in great numbers. According to Schätzel (1930, at 449 et seq; see Isidro and Hess, 2019, 247) by 1930 around 70,000 claims reached 36 MATs. A later overview by Hudson (1944, at 9) gave further details: the Polish-German MAT considered around 30,000 claims, the Franco-German MAT 20,000 claims, the Anglo-German MAT 10,000 claims (he also includes the American-German Mixed Claims Commission with around 13,000 claims but fails to mention the other MATs). Erpelding (2022, at 4) estimates that until 1939 around 100,000 claims had reached all 39 MATs. Most of these cases were, however, not decided by a formal written MAT-award following the submission of statement, response, réplique (reply), duplique (rejoinder), and oral proceedings. Rather, the overwhelming majority of claims were dealt with by compromises and other forms of claims-settlements negotiated between the government agents on behalf of their States. In order to accelerate the proceedings in light of the Allied mass claims, they concentrated their efforts on a number of important cases and included the majority of cases that seemed similar in fact and/or law in standardized claims forms to be prepared for compromises.

73  Nevertheless, the number of cases decided by the MAT-arbitrators were ‘far greater than that of the arbitral awards of all international arbitral tribunals that have been active up to now’ (‘weit größer als die der Schiedssprüche aller bisher tätig gewordenen internationalen Schiedsgerichte’ [translation by the author]) (Schlochauer, 1962, 26). Schätzel (1930, at 451) estimated that the larger tribunals, such as a division of the Franco-German MAT, managed to render 100 decisions per year, while, for example, the Romanian-German MAT had, after five years, only completed 76 cases (Göppert, 1931, 173). By 1930, the aggregate value of the sums awarded through MAT decisions and compromises was around Reichsmark 1 billion, while Allied claimants had demanded Reichsmark 3–4 billion from Germany.

74  The Paris peace treaties did not stipulate when the MATs would have to terminate their work. The RoPs set clear—and rather short—deadlines for all prospective claimants (see Rule 1 Anglo-German RoP 1920) or delais des présentation de requetes (Art 3 Franco-German RoP 1920). The general principle was that different classes of claims were being submitted to the MATs within six, 12 to 18 months ‘of the publication of these rules’ (claims under Art 297) or within 30 days of a decision of the clearing offices (Art 296 TV). Yet, irrespective of the intention of the authors of the MAT RoP to speedily come to a close with all MAT-related claims, there was always room left for exceptions. Rule 1 (d) Anglo-German RoP stipulated: ‘[a]fter the expiration of the times prescribed by this rule, no claim will be accepted without the special leave of the Tribunal’. Referring to principles of ‘equity’, a similar provision was included in Art 5 Franco-German RoP and the Tribunal used this competence repeatedly. The Franco-German MAT also formally decided again and again to extend its deadlines mentioned in the Rules of Procedure of 1920 to enable more individuals to file their claims (see the decision of the Franco-German MAT of 17 October 1921 to extend the deadline mentioned in Art 3 (c) of the Franco-German MAT RoP, in Oellers-Frahm and Zimmermann, 2001, 1627).

75  In line with its overall foreign policy goal to demolish the ‘Versailles order’, the German government had, since the mid-1920s, worked to convince its former enemies to replace the MAT apparatus with a diplomatic settlement of all claims. With the final approval of the ‘Young Plan’ at the second session of the Hague Conference on 20 January 1930, a new payment schedule for German reparation annuities was agreed. Furthermore, the Germans insisted that these negotiations about the ‘final liquidation of the war’ included all other claims based on the TV (including the liquidation of German property in Allied territories and thus the material base for the MAT proceedings). These claims were to be considered as replaced by the payments according to the Young Plan. In addition, Germany and Austria concluded several treaties with the neighbouring ‘new States’ agreeing that the remaining claims and counterclaims were to be settled or withdrawn from the MATs.

76  Though it was stated that ‘by the beginning of the 1930s, the work of these tribunals had come to an end’ (Wühler, 1981, 145), the actual work of the MATs continued in Istanbul or in Paris until around 1939—still dealing with, for example, French claims for ‘exceptional war measures’ (Art 297 (e) TV; Zollmann, 2021, 70; Boeg, 1937, 4). For a number of MAT members and also government agents the MATs became, over the course of 15-odd years, a ‘life’s work’ (Schätzel, 1955, 385, about the German government agent Robert Marx).

77  With the tens of thousands of claims that reached them, the MATs created an incalculable mass of case law that could be turned into precedents for subsequent decisions and into scholarly material that ‘dr[e]w the attention’ to complex open legal ‘questions’ (Lauterpacht, 2004 [1928], 405). Contemporaries looking back at the development of interstate arbitration since the First World War recognized the relevance of the Paris peace treaties for its further development and the ‘extensive practice’ of arbitration gained due to the MAT-provisions (Schindler, 1938, v). During the Second World War, scholars even began to look at the experience of the MATs to assess the means available under international law to demand ‘compensation for losses resulting from anti-racial measures’ from Germany (Goldschmidt, 1945, 101 et seq). Yet, instead of subsequent uses of case law produced by the MATs, this mass of precedents was—in the decades after the Second World War—‘largely forgotten’ (Crawford, 2010, 15), even though many jurists who had been involved in the work of the MATs were later involved in the establishment of the European Court of Justice (Erpelding, 2020, 454).

78  By contrast, it appears that, 100 years later, the scholarly analysis and ‘re-assess[ment]’ of the MAT judicature and the related RoP has begun—in a way fulfilling Lauterpacht’s (2004 [1928], at 405) prediction that the ‘long life’ of the disputes growing out of the First World War and its aftermath ‘will not have been in vain’. They put into the legal spotlight problems and questions of international dispute resolution that the MATs, the PCIJ, and also future courts of law and arbitration had to contend with. Among such problems were the central role of the individual in international law, the ‘efficient and fair’ handling of ‘mass claims’, and the adaptation and modernization of the rules of procedure for the use of interstate arbitration. In all these respects, still pertinent in the twenty-first century, the achievements of the MATs are to be seen in a ‘positive perspective’ (Isidro and Hess, 2019, 276).

79  At the moment of their inception, scholars were aware of the relevant role the MATs might play regarding an increased general political appreciation of interstate arbitration as a tool of international law that would include the rights of individuals. Mendelssohn Bartholdy (1922, at 45) made a plea to the Presidents of the MATs that they should ‘remember that these Mixed Arbitral Tribunals might show the worshipers of the State-idol how justice is not bound by boundary posts’ (‘eingedenk sein, daß diese Gemischten Schiedsgerichte den Anbetern des Staatsgötzentums zeigen könnten wie die Gerechtigkeit nicht an Grenzpfähle gebunden’ [translation by the author]). However, as has become clear throughout this article, the subsequent historical assessments of the ‘justice’ of the ‘economic clauses’ (Part X TV) of the peace treaties, including the judicature of the MATs, differed sharply between the victors and nationals of the defeated States. The ‘burdening of the postwar order with moral implications of guilt, crime and punishment’ (Leonhard, 2018, 31) was evident in the legal literature right from the moment of the conclusion of peace.

80  The break with the principle of the ‘inviolability’ of private ‘enemy property’ not only during but also after the war, as institutionalized by the Clearing Offices and the MATs, was criticized as being contrary to ‘the evolution of modern civilization’. Not only German, but also (rather pro-German) US lawyers expressed their ‘astonishment’ at Article 297 TV, since ‘at one stroke of the pen an institution which was deemed impregnable and fundamental to the existing economic order [the inviolability of private property] … was temporarily, at least, undermined. This cannot be deemed a service to mankind’ (Borchert, 1921, 523, 525). British and French lawyers, on the other hand defended these provisions of the peace treaties, arguing that ‘the world war upset many of the theories of international lawyers’ (Mullins, 1922, 92) and describing new institutions like the MAT as an ‘invocation of restorative justice’ (‘invocation de la Justice réparatrice’ [translation by the author]) (Jaudon in Gidel and Barrault, 1921, xxv) needed to (materially) heal the wounds of a war that Germany had started and lost.

81  It is clear that despite the one-sidedness of the MAT-system positive assessments of the idea and the practice of the MAT were not wholly absent from German legal literature, especially among the more liberally inclined authors. Strupp (1923, at 661) saw in the MAT ‘a real accomplishment, the fulfilment of wishes expressed even before the war’. Rabel (1929, at 62) welcomed an award of the Anglo–German MAT that had ‘instructed and instigated’ him. Even the German commissioner for the MAT Göppert (1931, at 172) lauded the Romanian-German MAT for a number of ‘excellently argued awards’ (‘ausgezeichnet begründeter Urteile’ [translation by the author]).

82  On the other hand, conservative German critics of what they saw as the ‘Western’ ideology of liberal internationalism with its legalistic tools—such as the MATs—and institutions—most of all the League of Nations—set up by the TV, remained unimpressed by the legal developments furthered by the case law and the procedures of the MAT. They mourned the creation of new ‘artificial’ States and within them German minorities through the means of an international law they considered patently unjust (Falk, 2020). For proponents of hegemonic structuring of international relations, with Germany as the hegemon of Central and Eastern Europe, the equality of States as exemplified in the MAT and the fact that the ‘newly States’ in Europe and their nationals could raise claims against their former overlords seemed offensive. Also in reputable legal publications, German authors spoke with regard to the meaning of the term ‘enemy’ in Allied laws during and after the war as serving an alleged Allied ‘war after the war’ against Germany (Held, 1924, 306); a ‘war’ they saw as also being waged by the one-sidedness of the provisions ruling the MATs.