1.  Notion

1  Cession is an understanding under international law by which territory is transferred from one State to another with the consent of both States. It is one of the modes by which States can lawfully acquire territory (Territory, Acquisition), and since it is based on mutual consent, it is presumably today the mode having the greatest practical relevance. As it necessarily entails a change of territory, cession entails a case of State succession, ie of the replacement of one State by another in the responsibility for the international relations of the territory (see Art. 2 (1) (b) Vienna Convention on Succession of States in Respect of Treaties [‘VCSS-T’]; State Succession in Treaties; Territorial Change, Effects of). It is described in Art. 15 VCSS-T as a situation where part of the territory of a State becomes part of the territory of another State. In slightly different words, and less precisely, Art. 14 (1) Vienna Convention on Succession of States in Respect of State Property, Archives and Debts (‘VCSS-PAD’) refers to the case when part of the territory of a State is transferred by that State to another State (State Succession in Other Matters than Treaties).

2  By always relating only to part of a State’s territory, cession must be distinguished from incorporation, which refers to the whole of a State’s territory becoming part of the territory of another State. Also, in the case of cession the territory concerned becomes integrated into the territory of an existing State; thus it is different from secession, where part of a State’s territory itself becomes an independent State. In a historical perspective, cession may also be distinguished from situations where territory is taken away from a State without its consent, as in the case of (partial) annexation or adjudication.

2.  Cession and Lease of Territory (‘Administrative Cession’)

3  The most important, and much more difficult, distinction has to be drawn between cession and the lease of territory (Territory, Lease), which is often referred to as ‘administrative cession’. Cession transfers full title to the territory concerned, in international legal terms the territorial sovereignty passes from one State to another. In contrast, when a State leases territory from another it simply receives the right to exercise the latter’s territorial authority (‘Gebietshoheit’) on the territory concerned, while full sovereignty remains as residual legal title with the original holder.

4  There are many well-known examples of territorial leases in international law, the most prominent for a long time being the 1898 lease of territory on the Chinese mainland north of Kowloon to the United Kingdom, which made the territory part of its Hong Kong colony: legally speaking those new territories always remained under Chinese territorial sovereignty, while their administration was granted to the British for 99 years. When the contractual lease expired in 1997, Hong Kong as a whole was given back to China on the basis of the Sino-British Joint Declaration of 1984 (1399 UNTS 33). The same legal regime applied to Macau, which after being leased to Portugal in 1887 was administered as a Portuguese colony until the People’s Republic of China resumed the exercise of sovereignty in December 1999.

5  Of some relevance today is the ongoing lease of territory on the island of Cuba to the United States: By two agreements of 1903 the Republic of Cuba leased to the US certain areas of land and water for the purpose of coaling and naval stations, among them some areas in Guantánamo Bay (USTS 418 and 426; Guantánamo Naval Base). Under those agreements, which are not subject to any time limit, the US shall exercise ‘complete jurisdiction and control’ over the areas concerned, while Cuba continues to hold the ‘ultimate sovereignty’ over them (at Art. III). Because of the latter it is not a case of cession. In 1934 the arrangement was confirmed and agreed to last ‘so long as the United States of America shall not abandon’ the naval station of Guantánamo (Treaty of Relations between the United States of America and the Republic of Cuba [signed 29 May 1934] USTS 866).

3.  Historical Examples

6  There are also quite a number of examples of proper cessions in the history of the law of nations. Some of them occurred on the basis of a sale contract, ie in exchange for the payment of money: thus the US bought Louisiana from France in 1803, Alaska from Russia in 1867, and the Philippines from Spain in 1898, although in the latter case the cession agreement contained in the Paris Peace Treaty simply ratified the conquest of the island State by US troops. Similarly, a cession may be agreed upon in exchange for another piece of territory: in 1890, the UK ceded Heligoland to Germany in exchange for Zanzibar. Many cessions were part of territorial re-arrangement contained in peace treaties, such as those concluded in 1919 (St Germain Peace Treaty [1919]; Versailles Peace Treaty [1919]) and 1947 with Italy, Finland, Roumania, and Hungary (Peace Treaties [1947]). In 1962 the Netherlands ceded the area of West-Irian, which they had held as a colonial possession, to Indonesia.

7  Today cessions normally concern small portions of territory along the borders. Thus, cession is the legal technique by which rectifications of boundaries between neighbouring States are being brought about, such as between Germany and, respectively, the Netherlands in 1960, 1980 and 1992, Belgium in 1982, Switzerland in 1964 and 2002, Austria in 1977, 1989 and 2001 and the Czech Republic in 2003.

1.  Legal Form

8  As cession requires the consent of both States involved, it normally takes place by means of a treaty or any other form of understanding. It is thus reminiscent of certain modes of transfer of ownership in private law. But since the concept of consent in international law is not dependent on certain formalities, cession may also be the object of a unilateral declaration by the grantor State which is accepted by the grantee. Such an understanding may also arise if the grantee is already in possession of the territory in question, although what happens then is more properly qualified as renunciation (Unilateral Acts of States in International Law).

9  An understanding of cession is always intended to be constitutive, ie to transfer legal title or to be the basis of such a transfer, while States may also conclude an agreement to settle a frontier or territorial dispute, which agreement would then probably be of a declaratory character. Also cession is always explicit and thus different from acquiescence, when a State does not protest against its territory being claimed or used by another State and thereby provides the basis for that territory being acquired by way of prescription.

2.  Validity

10  An act of cession can only be valid if both the State to which the territory has belonged so far and the State to which it is intended to belong in the future have declared their genuine consent, eg by concluding a treaty on that matter. Failing such consent by one of them, any arrangement of cession would be a res inter alios acta without legal effect vis-à-vis the non-consenting State. A consent procured through the use or threat of force is invalid according to Art. 52 Vienna Convention on the Law of Treaties (1969) (‘VCLT’; see also Use of Force, Prohibition of Threat), which reflects a generally recognized rule of customary international law (Fisheries Jurisdiction [UK v Iceland] (Jurisdiction) [1973] ICJ Rep 3 para. 24; Fisheries Jurisdiction Cases [United Kingdom v Iceland; Federal Republic of Germany v Iceland]).

11  On the other hand, the distribution of their own territory between two States is their sovereign prerogative and part of their domaine réservé. Thus, under international law, there is no requirement for a valid cession other than the sovereign will of the States concerned, and the exercise of that will is protected by the international rules of State sovereignty. A different question is, of course, whether the domestic law of one of the States involved contains legal preconditions for alterations to the State’s territory.

12  Apart from the prohibition of force, no other rules are recognized in present international law that would restrict the right of sovereign States to dispose of their territory, and the violation of which would result in an agreement of cession being null and void (Treaties, Validity). True, States can undertake—and indeed have undertaken in the past—an obligation not to cede or not to acquire a certain territory, or to do so only with the consent of an international body. But it seems that those obligations do not normally affect the title of the grantor State, thus their violation would render the cession illegal, but not invalid.

13  The question arises, though, whether certain parts of a State’s territory are by their very nature, and not by virtue of a special legal commitment, inalienable and thus cannot be validly ceded. A proposition of that kind has sometimes been put forward with reference to the territorial sea and the airspace above State territory. It appeared, for example, in the opinion of Judge McNair in the Fisheries Case (United Kingdom v Norway) when he pointed out that international law imposes upon a coastal State certain obligations arising out of its sovereignty over its territorial sea, and that, therefore, ‘the possession of this territory is not optional, not dependent upon the will of the State, but compulsory’ (at [1951] ICJ Rep 158, 160). But does that mean that a State can neither abandon nor cede its territorial waters to another State? The sovereign right of every coastal State to determine the breadth of its territorial sea (Art. 3 UN Convention on the Law of the Sea) and the right of two coastal States to determine their common maritime boundary by agreement (ibid Art. 15) would suggest that the coastal State is also in a position validly to dispose of the whole of its territorial sea.

14  If the preconditions for a valid cession are fulfilled, legal opinion is divided over the precise moment at which transfer of title occurs: on the entry into force of the relevant agreement or when effective possession is taken by the grantee. The better position seems to be that everything depends on the individual case and, above all, on the interpretation of the agreement concerned. Since cession is dependent on the sovereign will of the States concerned, it is up to them to decide on the moment when the transfer of territory takes effect. Because of the principle of effectiveness, however, that moment should not be before the coming into force of the relevant agreement; a provisional application of a treaty of cession is, therefore, not possible (Treaties, Provisional Application).

15  If the cession has been implemented by the two States, its effects are opposable to all third States (see also Treaties, Third-Party Effect). Because it is the sovereign right of the affected States to determine the legal status of their own territory and their common border, that determination, such as a transfer of territory to another State, develops effects erga omnes. All other States must be deemed to have implicitly recognized that right, so that they are precluded from invoking the res inter alios acta rule. If treaty rights of third States are adversely affected by the cession, they might claim reparation under the law of State responsibility.

3.  Issues of Legality

16  As pointed out previously (see para. 12 above), a treaty of cession may be in disregard of international obligations of one or both of the parties. Such violation would render the cession illegal for the State bound by that obligation, but would in principle not affect the validity of the cession as such. This could be different, however, if the treaty of cession was contrary to a norm of international ius cogens.

17  A controversial issue in legal doctrine has always been whether an acquisition of territory by cession presupposes the consent, or at least the consultation, of the population affected by the transfer of territory. In legal terms, it may be asked if such a requirement can be derived from the right of peoples to self-determination which today is universally recognized as a rule of customary international law. At least two major problems arise here. First, in order to be entitled to self-determination, ie to qualify as ‘people’ within the meaning of that rule, a group of human beings must be characterized by at least one common feature which binds them together as a homogenous group. It is very doubtful whether to live on a common territory alone can be considered such a feature: population does not constitute a people. Secondly, and more importantly, international practice does not seem to regard the will of the population as decisive for the legality of cessions or other territorial changes. Although the idea of plebiscites (Plebiscite) had been put forward at the end of World War I, subsequent practice in the wake of both World Wars, as well as at the demise of the Soviet Union and Yugoslavia (Yugoslavia, Dissolution of), did not follow that idea and did not inquire about the consent of any population of the territories concerned.

18  However, in its recent advisory opinion on the Chagos Archipelago (Chagos [Advisory Opinion]), the International Court of Justice (ICJ) held that, at least in the context of decolonization of non-self-governing territories, self-determination entails a right to the territorial integrity of those territories, and that, therefore, any detachment by the administering Power of part of a non-self-governing territory, unless based on the freely expressed and genuine will of the people of the territory concerned, is contrary to the right to self-determination (at para. 160). The Court considered, therefore, that the detachment in 1965 of the Chagos Archipelago from the British colony Mauritius and its incorporation into the newly created British Indian Ocean Territory was unlawful. Applying that opinion to the case of cession, one might make the argument that ceding a part of a non-self-governing territory to a third State, without the consent of the people concerned, would also be illegal under international law.

1.  Responsibility for Territory

19  The immediate effect of cession is the transfer of the responsibility under international law for the territory in question. Upon the title passing to the grantee, everything that happens on the territory is legally attributable to that State, the latter being responsible vis-à-vis other States for every damage that may arise from acts or the failure to act on that territory. That includes, for example, the obligation under international law to prevent environmental harm to another State’s territory (Liability for Environmental Damage; Trail Smelter Arbitration; see also Air Pollution, Transboundary Aspects) or the obligation to make sure that the territory is not used for private acts of violence against other States (Responsibility of States for Private Actors).

2.  State Succession in Respect of Treaties

20  Under the rules of State succession with respect to treaties the so-called principle of moving treaty frontiers applies: according to Art. 15 VCSS-T, the treaties of the predecessor State (grantor) cease to apply to the territory concerned from the date when the cession takes effect, and the treaties of the successor State (grantee) come into force in respect of that territory. Thus, the scope of application of a State’s treaties follows in principle every extension or reduction of that State’s territory, which is exactly what already follows from Art. 29 VCLT.

21  Exceptions to the rule are also laid down in Art. 15 VCSS-T. The moving treaty frontiers rule does not apply when it would be incompatible with the object and purpose of the treaty in question, or if it would radically change the conditions for its operation (Treaties, Object and Purpose). One example is treaties establishing territorial regimes on the ceded territory, such as servitudes for the benefit of third States or of all States: obligations deriving from those treaties for the predecessor State would certainly be transferred with the territory to which they relate on to the successor State (see Art. 12 VCSS-T).

22  Also international practice, eg with regard to the transfer of Hong Kong to China, although only in part a proper cession, suggests that the two States involved may agree upon exceptions to the moving treaty frontiers rule and, for example, determine that certain treaties of the predecessor State will continue to apply or that some treaties of the successor State will not (immediately) apply to the ceded territory.

3.  State Succession in Respect of Property and Debts

23  The cession of State territory may also be a reason for the passing of State property and of State debts of the predecessor to the successor State. In principle, such passing is to be settled by agreement between the two States. In the absence of such an agreement Art. 14 (2) VCSS-PAD, which is not in force, stipulates that immovable property situated in the territory and movable State property ‘connected with the activity of the predecessor State in respect of the territory’ shall pass to the successor State. Also an equitable portion of the State debt shall pass to the successor State, taking into account the relation of the State debt to the property, rights and interests which pass to the successor (Art. 37 (2) VCSS-PAD). Apart from State debts, it appears that under customary international law so-called local debts, which are owed by local authorities with a certain financial autonomy, remain their responsibility in application of the principle res transit cum onere suo.

4.  Nationality of Individuals

24  One of the most important issues of State succession for private individuals is the question of their nationality. While the population of the ceded territory does not as a matter of international law ipso facto change its nationality, it will again be open to the two States concerned to conclude an agreement on that issue and to adopt corresponding national legislation. Naturally, any agreement between them can only extend to their own nationalities, not to those of third States.

25  In the absence of an agreement, the successor State will normally have the right to extend, as it does its entire legal order, its nationality to those persons among the newly acquired population that were hitherto nationals of the predecessor State. Until such legislation is enacted, the 1999 Draft Articles by the International Law Commission (ILC) on Nationality of Natural Persons in relation to the Succession of States (‘ILC Draft Articles’) propose in Art. 5 to apply a rebuttable presumption that persons having their habitual residence in the territory concerned acquire the nationality of the successor State. The Council of Europe Convention of 2006 on the Avoidance of Statelessness in Relation to State Succession (‘CoE Convention’) follows a different approach and establishes an obligation of the successor State to grant its nationality to nationals of the predecessor State who would become stateless as a result of the State succession (Stateless Persons), if these persons were either habitually resident in the territory in question or had an ‘appropriate connection’ with the successor State (Art. 5 CoE Convention).

26  As a consequence of succession, the nationals of the predecessor State resident in the territory concerned should be presumed to lose their old nationality. The ILC Draft Articles, however, in reflecting prevailing State practice, stipulate that in the case of a cession the loss of nationality does not happen ipso facto upon succession, but only upon constitutive withdrawal by the predecessor State, and that the latter is normally under a duty to do so (Art. 20 ILC Draft Articles). Similarly, Art. 6 CoE Convention prohibits the predecessor State from withdrawing its nationality from persons who would otherwise become stateless.

27  Although the right to self-determination and the international protection of human rights have certainly led to greater consideration of the interests of the individual, customary international law has not (yet) developed an obligation of the successor State to grant a right of option to the persons concerned. Art. 20 ILC Draft Articles, however, proposes that such a right ‘shall be granted’ by both States, which the ILC itself explicitly considers to entail a progressive development of international law (ILC Commentary on Draft Art. 20 para. 5; Codification and Progressive Development of International Law). As a general rule de lege lata, Art. 11 (2) ILC Draft Articles sets out the obligation of each State to grant a right to opt for its nationality to persons who would otherwise become stateless as a result of the succession of States. Slightly more cautious, Art. 7 CoE Convention requires the successor State to respect the expressed will of persons to acquire its nationality.

Select Bibliography

• DP O’Connell The Law of State Succession (CUP Cambridge 1956).

• DP O’Connell State Succession in Municipal Law and International Law (CUP Cambridge 1967).

• G Dahm J Delbrück and R Wolfrum Völkerrecht vol 1.1 Die Grundlagen. Die Völkerrechtssubjekte (2^nd edn Walter de Gruyter Berlin 1989) 370–76.

• A Zimmermann Staatennachfolge in völkerrechtliche Verträge: Zugleich ein Beitrag zu den Möglichkeiten und Grenzen völkerrechtlicher Kodifikation (Springer Heidelberg 2000).

Select Documents

• CoE ‘Convention on the Avoidance of Statelessness in Relation to State Succession’ (done 19 May 2006, entered into force 1 May 2009) CETS No 200.

• Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 (Advisory Opinion) (25 February 2019) ICJ Doc 2019 General List No 169.

• UN ILC ‘Draft Articles on Nationality of Natural Persons in Relation to the Succession of States’ (1999) GAOR 54^th Session Supp 10, 15.

• United Nations Convention on the Law of the Sea (concluded 10 December 1982, entered into force 16 November 1994) 1833 UNTS 3.

• Vienna Convention on the Law of Treaties (concluded 23 May 1969, entered into force 27 January 1980) 1155 UNTS 331.

• Vienna Convention on Succession of States in Respect of State Property, Archives and Debts (done 8 April 1983, not in force) 22 ILM 298.

• Vienna Convention on Succession of States in Respect of Treaties (concluded 23 August 1978, entered into force 6 November 1996) 1946 UNTS 3.