Original version by Gerhard Hafner December 2006; reviewed by Gerhard Hafner November 2024.

A.  Background to the Advisory Opinion

1  Towards the end of World War I, Great Britain occupied large parts of the vilayet (region) Mosul, formerly under the rule of the Ottoman Empire, and set up a civil administration in this area (Occupation, Belligerent; Occupation, Pacific). Subsequently, Great Britain received Mesopotamia, including Mosul, as mandate under the system of Article 22 Covenant of the League of Nations (1919) (League of Nations; Mandates). The Treaty of Peace between the Allied and Associated Powers and Turkey signed at Sèvres of 10 August 1920 that defined the northern boundary of the vilayet Mosul as the frontier between Mesopotamia—later becoming Iraq—and Turkey never entered into force. During the fresh negotiations that were started with the new Turkish regime in Lausanne in 1920, the question of the boundary between Turkey and Mesopotamia in the region of Mosul became the object of a dispute between Turkey and Great Britain. Since no solution was achieved during the negotiations, Article 3(2) Treaty of Peace with Turkey signed at Lausanne (‘Treaty of Lausanne’) of 24 July 1923 provided that the ‘frontier between Turkey and Iraq shall be laid down in friendly arrangement to be concluded between Turkey and Great Britain within nine months’ and that in ‘the event of no agreement being reached between the two Governments within the time mentioned, the dispute shall be referred to the Council of the League of Nations’ (History of International Law, World War I to World War II; Lausanne Peace Treaty (1923)).

2  When, following the eventual failure of the negotiations between Great Britain and Turkey, this matter was brought before the Council of the League of Nations where Turkey was represented even though not a member of the League of Nations, a dispute arose between these two States concerning the interpretation of this passage of the Treaty of Lausanne (Interpretation in International Law). Agreement was reached to request the Permanent Court of International Justice (PCIJ) for an advisory opinion on the following questions:

3  Irrespective of the fact that Turkey had not accepted the jurisdiction of the Court, the latter complied with this request for an advisory opinion since this request came from the Council and did not address the issue of the drawing of the boundary line, but a matter of the competence of the Council (Advisory Opinions; International Organizations or Institutions, Decision-Making Bodies).

B.  Opinion of the PCIJ

4  The gist of the advisory opinion of the Court of 21 November 1925 concerned the interpretation of treaties, notably the Treaty of Lausanne and the Covenant of the League of Nations. The Court proceeded from the basic view that the common will of the parties, reflected in the treaty, had to be sought in the conventional text: first in the clause under scrutiny, subsequently in the context. If the construction of the text according to this method of interpretation was clear, no resort to the travaux préparatoires was needed, even if only to confirm the interpretation already achieved.

5  The PCIJ also took into account the objective of the treaty, since it came to the conclusion that the objective of Article 3 Treaty of Lausanne to establish the frontier was to be derived from the wording of this article—‘the frontier should be laid down’—as well as from the intention of the parties to ‘establish a situation which would be definitive’ (Interpretation of Article 3, Paragraph 2, of the Treaty of Lausanne (Frontier between Turkey and Iraq) (Advisory Opinion) (1925) 20). The context strengthened this conclusion since Article 16 Treaty of Lausanne also referred to the frontier ‘laid down in the present Treaty’. No reference could be made to travaux préparatoires such as various statements delivered during the negotiation process since they did not reveal any agreement, otherwise the PCIJ would have to act as a mediator (Mediation). As the Court was asked to interpret Article 3 Treaty of Lausanne as it was established at the time of the conclusion of the treaty, subsequent practice as reflected in the discussions and negotiations between the mostly interested states was outside the scope of the matter put before the Court.

6  Regarding the legal nature of the decision on the drawing of the boundary to be reached by the Council, the PCIJ derived from the objective under Article 3 Treaty of Lausanne that the Council had to come to a definitive and binding decision. Article 15 Covenant of the League of Nations, which entitled the Council to adopt only recommendations, set out merely minimum obligations and corresponding powers of the Council. These powers were supplemented by the Treaty of Lausanne that, in the light of its objective to decide on the frontier, entitled the Council, in addition to the functions under the Covenant of the League of Nations, to establish a decision binding upon the parties. According to the Court, ‘[i]t is … natural that any article designed to fix a frontier should, if possible, be so interpreted that the result of the application of its provisions in their entirety should be the establishment of a precise, complete and definitive frontier’ (at 20).

7  The PCIJ further examined whether the decisions of the Council were subject to the unanimity rule and whether the representatives of the interested states were entitled to take part in the vote (International Organizations or Institutions, Voting Rules and Procedures). Since the matter was conferred upon the Council as an organ of the Covenant of the League of Nations and the Treaty of Lausanne did not provide otherwise, the rule of unanimity applied as required in Article 5 Covenant of the League of Nations. This rule of decision-making not only applied to the functions derived from the covenant but operated as a general rule. The majority rule being typical for arbitral awards, to which Great Britain referred, did not apply since the Council did not act as an arbitral tribunal (Arbitration).

8  As to the voting rights, the Court referred to Article 15(6) and (7) Covenant of the League of Nations according to which the votes cast by the representatives of the interested parties did not affect the required unanimity. In the Court’s view the rule of unanimity that applied to the recommendations under this article should a fortiori also apply to situations where binding decisions had to be taken by the Council. This solution was deemed to correspond to the principle nemo iudex in causa sua (no man may be a judge in his own cause; translation by the editor). Otherwise the interested parties would have a veto power that was not envisaged by Article 3(2) Treaty of Lausanne (Veto).

9  For these reasons, the PCIJ concluded that the decision to be taken by the Council of the League of Nations pursuant to Article 3(2) Treaty of Lausanne had a legally binding effect and constituted a definite determination of the frontier between Turkey and Iraq and that this decision had to be taken by unanimous vote, subject to the condition that the votes of the representative of interested parties did not affect the unanimity.

C.  Continuing Relevance of the Opinion

10  The continuing significance of this advisory opinion is twofold. On the one hand, it paved the way to the rule on interpretation according to Articles 31 and 32 Vienna Convention on the Law of Treaties (1969) according to which the will of the parties to a treaty has to be derived from the text of the treaty whereas the travaux préparatoires are only a subsidiary means of interpretation (Textual Interpretation). On the other hand, in its judgment of 3 February 1994 in the Territorial Dispute Case (Libyan Arab Jamahiriya/Chad), the International Court of Justice (ICJ) referred to the reasoning of the PCIJ according to which the objective of a treaty to lay down a boundary line implied the necessity to achieve a binding decision.