A.  Notion

1  Annexation means the forcible acquisition of territory by one State at the expense of another State. It is one of the principal modes of acquiring territory (Territory, Acquisition; see also Occupation, Belligerent). Annexation presupposes the effective occupation of the territory in question and the clear intention to appropriate it permanently (corpus et animus). Either parts of another State or its entire territory can be annexed. Annexation is in contrast to acquisition a) of terra nullius by means of effective occupation accompanied by the intent to appropriate the territory (Occupation, Pacific); b) by cession as a result of a treaty concluded between the States concerned (Treaties), or an act of adjudication, both followed by the effective peaceful transfer of territory; c) by means of prescription defined as the legitimization of a doubtful title to territory by passage of time and presumed acquiescence of the former sovereign; d) by accretion constituting the physical process by which new land is formed close to, or becomes attached to, existing land. Under present international law, annexation no longer constitutes a legally admissible mode of acquisition of territory as it violates the prohibition of the threat or use of force (Use of Force, Prohibition of). Therefore annexations must not be recognized as legal.

2  Under previous international law, annexation was usually effected by a unilateral declaration after the conquest of the territory in question and the final defeat of the adversary (see also Unilateral Acts of States in International Law). If either element was missing, there was no effective annexation. Final defeat of the adversary presupposed either the complete destruction of the enemy State (States, Extinction of) or the existence of a situation in which hostilities could no longer be continued (Debellatio) since international law recognized—and still recognizes—that war can be terminated not only by the conclusion of a peace treaty but also by the mere but final cessation of hostilities (Armed Conflict, International). With a declaration of annexation, a State announced its intention of acquiring the territorial sovereignty, and not only jurisdiction, over the territory in question; without any such clear declaration of intent, there was no effective annexation.

3  Annexation could also be effected by the conclusion of a treaty. Unlike other treaties concerning territorial changes, such treaties involved an element of compulsion. This means that the ceding State had been forced to sign a peace treaty after a military defeat or to agree to a transfer of territory as a consequence of a threat of force or that it had been represented by a puppet government prepared to accept the annexation. In contrast to the situation under present international law, such use of compulsion or the involvement of a puppet government were previously not considered as sufficient grounds to render the treaty in question legally invalid (Treaties, Validity); consequently, such annexations were held to be in compliance with applicable international law.

B.  Historical Evolution of Legal Rules

4  As long as general international law did not prohibit the threat or use of force in international relations, annexation was considered to constitute a legally valid mode of acquisition of territory. This situation began to change subsequent to the conclusion of the Kellogg-Briand Pact (1928). Today, as stipulated by Art. 2 (4) United Nations Charter (‘UN Charter’), not only war, but also the threat or use of force in any form constitutes, in principle, an internationally wrongful act from which no rights may be derived (ex iniuria jus non oritur); consequently, annexations are illegal.

C.  Current Legal Situation

16  This position is also confirmed by subsequent consistent State practice. Various resolutions of the United Nations General Assembly (United Nations, General Assembly; ‘General Assembly’) and the United Nations Security Council (United Nations, Security Council; ‘Security Council’) confirm this viewpoint. Already in 1967, Security Council Resolution 242 (1967) emphasized the ‘inadmissibility of the acquisition of territory by war’ (UNSC Res 242 [22 November 1967] UN Doc S/RES/242 [1967]). Although they are not to be regarded as binding international law, General Assembly resolutions show how States interpret the prohibition of the use of force and its consequences. The Friendly Relations Declaration (1970) declares, within the scope of the principle forbidding the use of force, that ‘the territory of a State shall not be the object of acquisition by another State resulting from the threat or use of force. No territorial acquisition resulting from the threat or use of force shall be recognized as legal.’ This is also confirmed by Art. 5 (3) General Assembly Resolution 3314 (XXIX) on the Definition of Aggression, which states that ‘[n]o territorial acquisition or special advantage resulting from aggression is or shall be recognized as lawful’. Moreover, the principle of sovereign equality of States (States, Sovereign Equality) includes territorial integrity as one of its elements and states that this is inviolable. In its Arts 4 and 5, the Declaration on the Strengthening of International Security (UNGA Res 2734 [XXV]) reaffirms this solemnly. On the regional level, the Helsinki Final Act (1975) recognizes in its principles I–IV the sovereign equality of all States, the obligation of States to refrain from the threat or use of force, as well as the inviolability of frontiers and the territorial integrity of States and, thereby, adds to the general ban on annexation as a lawful means for acquisition of territory.

17  The illegality under international law of any annexation based on an unauthorized use of force was also confirmed by developments in connection with the occupation and annexation of Kuwait by Iraq (Iraq-Kuwait War [1990–91]). Security Council Resolution 662 (1990) unanimously declared Iraq’s annexation of Kuwait to be null and void and called upon States and institutions not to recognize the annexation and to refrain from any action that might be interpreted as an indirect recognition of it. Moreover, the European Community, in its Guidelines on the Recognition of New States in Eastern Europe and in the Soviet Union, adopted as a common position on 16 December 1991 in Brussels, established as one condition for such recognition the ‘respect for the inviolability of all frontiers which can only be changed by peaceful means and by common agreement’ and confirmed that it would not recognize entities that ‘are the result of aggression’.

18  Attention should also be drawn to Art. I of the General Framework Agreement for Peace in Bosnia and Herzegovina (Dayton Agreement) in which the States Parties to that treaty explicitly recognized their obligations to ‘fully respect the sovereign equality of one another’ and ‘to refrain from any action, by threat or use of force or otherwise, against the territorial integrity or political independence of Bosnia and Herzegovina or any other State’; moreover, in Art. X, the Federal Republic of Yugoslavia and the Republic of Bosnia and Herzegovina agreed to ‘recognize each other as sovereign independent States within their international borders’. The strong commitment of the international community to outlaw annexations is also reflected in numerous Security Council Resolutions, eg Resolution 1244 (1999), establishing international civil and security presences in Kosovo, which reaffirms, in its preamble, ‘the commitment of all Member States to the sovereignty and territorial integrity of the Federal Republic of Yugoslavia and the other States of the region’ (UNSC Res 1244 [1999] [10 June 1999] UN Doc S/RES/1244 [1999]), or Resolution 1472 (2003) on the situation in Iraq which reaffirms, in its preamble, ‘the commitment of all member states to the sovereignty and territorial integrity of Iraq’ (UNSC Res 1472 [2003] [28 March 2003] UN Doc S/RES/1472 [2003] ; Iraq, Occupation after 2003).

19  Moreover, Art. 52 Vienna Convention on the Law of Treaties (1969) (‘VCLT’) states that a treaty is void ‘if its conclusion has been procured by the threat or use of force in violation of the principles of international law embodied in the Charter of the United Nations’ and, thus, rejects the validity of even a treaty-based annexation.

20  Finally, the obligation of third States not to recognize as lawful any territorial changes brought about by means of annexation can also be based upon Art. 41 (2) draft articles on the Responsibility of States for internationally wrongful acts of the International Law Commission (ILC), according to which States must not recognize as lawful a situation created by a serious breach of an obligation arising under a peremptory norm of general international law, nor render aid or assistance in maintaining that situation (State Responsibility).

21  In view of the pertinent consistent and uniform State practice it is beyond any doubt that, under present international law, the prohibition of annexation and the obligation not to recognize it as lawful (Stimson Doctrine) extend beyond treaty obligations and form part of customary international law. Considering the essential relevance of these two principles in terms of the effective implementation of the prohibition of the threat or use of force as the most fundamental norm of present international law, there are convincing reasons to consider them as ius cogens norms.

D.  Specific Legal Problems

22  Notwithstanding the unequivocal prohibition of annexation and the corresponding equally clear obligation not to recognize it as legal, there remain some specific legal problems. The most relevant concerns the question of whether the annexation of territory of an aggressor State might, as an exception to the general rule, be considered lawful under present international law and whether an initially unlawful annexation may be turned into a lawful cession of territory by the subsequent conclusion of a (peace) treaty. Moreover, it might be argued that the factual recognition by the international community of an unlawful annexation eventually results in the lawfulness of the territorial change in question. Finally, the legal situation of the population of the territory annexed raises a number of intricate questions.

E.  Some Past and Present Issues

31  As concerns the legal situation of Germany after 1945 Germany, Occupation after World War II), it is important to note that the assumption of supreme authority with respect to Germany by the Four Powers by their declaration of 5 June 1945 was clearly not intended to effect the annexation of Germany. Then, it was decided at the Potsdam Conference (1945) to determine a special status for parts of the Soviet zone of occupation by placing under the administration of the Soviet Union the northern part of East Prussia including the city of Königsberg (now Kaliningrad Oblast), and by placing under the administration of the Polish State all other German territories east of the Oder-Neisse Line. The legal status of these territories was the subject of some controversy. Unlike the German Democratic Republic and her socialist allies, the Federal Republic of Germany insisted that a final settlement could only be agreed with a unified Germany (Germany, Unification of). This final settlement was brought about by the Treaty on the Final Settlement with respect to Germany (Two-plus-Four Treaty) of 12 September 1990: the existing outer frontiers of the two German States were declared to be final, and Germany undertook not to raise any territorial claims. The pertinent formal German-Polish Boundary Treaty, signed on 14 November 1990, entered into force on 16 January 1992.

32  The Baltic States of Estonia, Latvia and Lithuania were incorporated into the Soviet Union in early August 1940 following their military occupation by Soviet troops in June 1940. Since this incorporation was not based on a free expression of the will of the peoples concerned, most Western countries considered this incorporation as an unlawful annexation and did not give de iure recognition of Soviet sovereignty over the Baltic countries whereas all socialist countries and most developing countries gave such de iure recognition. Under the reform policy introduced by Gorbachev, the population of the Baltic States began to demand true national sovereignty. On 16 November 1988, the Estonian Parliament adopted the Declaration on the Sovereignty of Estonia which was followed by similar declarations in Lithuania and Latvia on 18 May 1989 and 28 July 1989, respectively. Finally, on 6 September 1991, the Soviet Union formally recognized the independence of the three Baltic States and, thus, terminated the unlawful annexation. Fully in line with present international law, the three Baltic States consider that these acts have only restored their full sovereignty, which had been lost in 1940, and do not consider themselves as newly independent States.

33  Whereas the State practice concerning the Baltic States had been inconsistent, the international community reacted quite differently in reference to annexations effected by Israel concerning Jerusalem and the Golan Heights. Subsequent to the cessation of hostilities in 1949, the international community did not give de iure recognition to the annexation of West Jerusalem by Israel but only recognized that Israel exercised de facto authority in the part of the city under its control. Largely the same view was taken with respect to the annexation, in 1949, of East Jerusalem by Jordan. The steps taken by Israel to incorporate, after the June 1967 war, East Jerusalem were rejected as illegal acts of annexation unable to alter the status of the city under international law. This is clear from the pertinent resolutions adopted by both the General Assembly (see, for example, Resolutions 2253 [ES-V] and 2254 [ES-V]) and the Security Council (see, in particular, Resolution 252 [1968]). This position has been consistently upheld in later resolutions. As concerns the annexation of the Golan Heights by Israel effected by virtue of its Law on Golan Heights of 14 December 1981, the Security Council decided, in its Resolution 497 (1981), that the ‘Israeli decision to impose its laws, jurisdiction and administration in the occupied Syrian Golan Heights is null and void and without international legal effect’ (UNSC Res 497 [1981] [17 December 1981] UN Doc S/RES/497 [1981]). A similar view was taken by the General Assembly in its Resolution ES-9/1 of 8 February 1982. Until now, there have been no changes in the position of the international community, which continues to consider the annexation of the Golan Heights unlawful.

34  Whereas the illegality of annexation has been of central relevance for the assessment of the legal position of the Baltic States under Soviet occupation and continues to be so as regards Jerusalem and the Golan Heights, there are situations which are predominantly discussed in the light of the right of peoples to self-determination notwithstanding that they involve elements related to acts constituting annexation. Pertinent examples include East Timor, Tibet and the (Western) Sahara.

35  In contrast to the former Dutch colony of Western New Guinea (West-Irian), the territorial status of which as a province (Irian Barat) of Indonesia has been accepted by the international community (see UNGA Res 2504 [XXIV] [20 November 1969] UN Doc A/RES/2504 [XXIV]) notwithstanding some reservations as to the fairness of the collective consultations held in summer 1969 as the final step to implement an agreement signed on 15 August 1962 (Agreement between the Republic of Indonesia and the Kingdom of the Netherlands concerning West New Guinea [West Irian] [signed 15 August 1962] 437 UNTS 273) under which the territory had been, first, transferred from Dutch administration to a United Nations Temporary Authority and, on 1 May 1963, placed under the administration of Indonesia (Decolonization: Dutch Territories), the international community never accepted the acquisition of the former Portuguese colony of East Timor by Indonesia (see also Decolonization: Portuguese Territories). Subsequent to the withdrawal of the Portuguese forces in summer 1975, Indonesian armed forces had invaded the area which was later annexed by Indonesia. This act, which was based on the argument that Portugal had abandoned the territory, was, however, never recognized as legally valid by the international community which, in a series of General Assembly (see eg Resolution 3485 [XXX]) and Security Council (see eg Resolution 384) Resolutions, demanded that Indonesia recognize the right of the Timorese people to self-determination and withdraw its troops from the territory of East Timor. Consequently, the nominal status of East Timor in the United Nations (UN) remained that of a non-self-governing territory under Portuguese administration (Non-Self-Governing Territories). After years of bitter guerrilla warfare (Guerrilla Forces) and following the conclusion, on 5 May 1999, of agreements between Indonesia, Portugal and the UN, the East Timorese population expressed, in a consultation held on 30 August 1999, its wish to begin a process towards independence. This, however, was only achieved as a result of the establishment, by Security Council Resolution 1272 (1999), of the UN Transitional Administration in East Timor (‘UNTAET’). On 22 May 2002, East Timor became an independent State and, on 27 September 2002, joined the UN.

36  Whereas the 1951 incorporation of Tibet as an autonomous region into China has been seen by some authors as an unlawful annexation, China consistently maintains that Tibet had always been an integral part of China and never an independent territory. This situation reflects the fact that the historical status of Tibet has always been most controversial. Notwithstanding the issue of the compatibility with international law of the 1951 act of incorporation as allegedly being an act of annexation, the question remains as to whether this act and the subsequent exercise of sovereignty by China over Tibet constitute a violation of the right to self-determination of the Tibetan population. It must be seen, however, that, notwithstanding an increase of public attention as concerns the situation in Tibet subsequent to the award of the Nobel Peace Prize to the Dalai Lama in 1989, this issue is pursued mainly by the governments of Western States, as part of their human rights dialogue with the Chinese government, and a number of non-governmental organizations (Human Rights, Role of Non-Governmental Organizations), but has not been the subject of any General Assembly Resolution since the adoption of Resolution 2079 (XX) in 1965. The Chinese government has always maintained that the principle of self-determination is not applicable to Tibet as it was never subject to a colonial regime. This might also explain why Tibet was never entered onto the General Assembly list of non-self-governing territories.

37  The legal situation of the (Western) Sahara raises similarly intricate problems. They concern, however, not so much the question of whether the incorporation of this territory into Morocco is to be qualified as an unlawful annexation but rather the question of whether this act of incorporation violates the right to self-determination of the Sahrawi population. At the outset, it should be recalled that the ICJ, in its Advisory Opinion on certain legal aspects of the territory at the time of colonization (Western Sahara, 1975 ICJ Rep 12; Western Sahara [Advisory Opinion]), had held that the territory of the Western Sahara could not be considered terra nullius and that neither Mauritania nor Morocco had exercised territorial sovereignty over Western Sahara notwithstanding the existence of certain legal ties in a broader sense. However, these legal ties were not of such a nature as to prevent the decolonization of Western Sahara and the exercise of the right to self-determination by the Sahrawi people in accordance with the provisions of the General Assembly Resolution 1514 (XV) (Declaration on the Granting of Independence to Colonial Countries and Peoples). Notwithstanding this Advisory Opinion, Mauritania, Morocco and Spain concluded, on 14 November 1975, a tripartite treaty, dividing Western Sahara between Mauritania and Morocco (Declaration of Principles on Western Sahara by Spain, Morocco and Mauritania), which resulted in the occupation of most of the Western Sahara by Mauritanian and Moroccan troops and the integration of these territories into Mauritania and Morocco, respectively, subsequent to the Spanish withdrawal in February 1976. This was opposed by the Frente Popular para la Liberación de Sagia el Hamra y Rio de Oro (Frente Polisario) which began an armed struggle against the Mauritanian and Moroccan forces and proclaimed, on 27 February 1976, Western Sahara as the Sahrawi Arab Democratic Republic (‘SADR’). After Mauritania had abandoned, in 1979, its claims on the southern part of the Western Sahara, most of its territory is now administered by Morocco but sovereignty remains unresolved with the UN attempting—so far without success—to hold a referendum on the issue through the UN Mission for the Referendum in Western Sahara (‘MINURSO’) (established by Security Council Resolution 690 [1991]; the mandate of MINURSO has been continuously extended and is, at present, based on Security Council Resolution 2044 [2012], adopted on 24 April 2012). A cease-fire, administered by the UN and implemented by MINURSO, has been in effect since September 1991. At present, the UN still considers Western Sahara as a case of incomplete decolonization and keeps it on its list of non-self-governing territories (see UNGA ‘Report of the Special Committee on the Situation with regard to the Implementation of the Declaration on the Granting of Independence to Colonial Countries and Peoples for 2011’ UN Doc A/66/23 GAOR 66^th Session Supp 23 paras 115–19). The African Union (AU)—formerly Organization of African Unity—has given the SADR full recognition and accepted it, in 1984, as a Member State which has led Morocco to leave this organization. Morocco considers all of Western Sahara as an integral part of the Kingdom while Polisario maintains that it is an occupied territory. Information as to the number of States which have recognized the SADR (or recently withdrawn or frozen such previous recognition) varies considerably; at present, most sources indicate that there are more than 50 States which continue to recognize the SADR. It is not a Member State of the UN, but on 21 November 1979, the General Assembly recognized in its Resolution 34/37 Polisario as the representative of the Sahrawi people. Moroccan sovereignty over the territory is supported, but not formally recognized, by the League of Arab States (LAS) and some 50 States.

F.  Evaluation

38  Under present international law, annexations are illegal since they are incompatible with the most fundamental rule on the prohibition of any threat or use of force. As such, they do not result in a lawful title to territory. All States are under a legal obligation not to recognize annexations and their consequences as lawful. They may, however, give some de facto recognition to unlawful annexations in order to accommodate adequately the needs of the inhabitants of the annexed territory. There are good reasons to consider the prohibition of annexations and the obligation not to recognize them and their consequences as lawful as rules of customary international law with the rank of ius cogens.