Acquisition of sovereignty
A state may acquire sovereignty over territory if that sovereignty is ceded (transferred) to it by another state. Cession is typically effected by treaty. Examples of cession include the cession of Hong Kong Island and Kowloon, purchases such as the Louisiana Purchase and the Alaska Purchase, and cessions involving multiple parties such as the Treaty on the Final Settlement with Respect to Germany.
Since the emergence of self-determination as a recognised principle of international law, a state may need to consult the inhabitants of a territory (if any) before they may cede sovereignty over it.
In the case of United States v. Huckabee (1872), the US Supreme Court speaking through Mr. Justice Clifford, said: "Power to acquire territory either by conquest or treaty is vested by the Constitution in the United States. Conquered territory, however, is usually held as a mere military occupation until the fate of the nation from which it is conquered is determined .... " Such a legal rationale naturally applies to all sovereign governments.
Direct annexation, the acquisition of territory by way of force, was historically recognised as a lawful method for acquiring sovereignty over newly acquired territory before the mid-1700s. By the end of the Napoleonic period however, invasion and annexation ceased to be recognized by international law and were no longer accepted as a means of territorial acquisition. The Convention respecting the Laws and Customs of War on Land (Hague IV, 1907) contained explicit provisions concerning the protection of civilians and their property in occupied territories. The United Nations Charter also has related provisions.
In the words of the International Awards in the case of Eritrea:
- The modern international law of the acquisition (or attribution) of territory generally requires that there be: an intentional display of power and authority over the territory, by the exercise of jurisdiction and state functions, on a continuous and peaceful basis.
Also in the case of Mexico and France over Clipperton Island:
- It is beyond doubt that by immemorial usage having the force of law, besides the animus occupandi, the actual, and not the nominal, taking of possession is a necessary condition of occupation. This taking of possession consists in the act, or series of acts, by which the occupying state reduces to its possession the territory in question and takes steps to exercise exclusive authority there.
In the case of Netherlands and the United States in the Islands of Palmas case, the arbitrator ruled:
- The title of discovery... would... exist only as an inchoate title, as a claim to establish sovereignty by effective occupation. An inchoate title however cannot prevail over a definite title founded on continuous and peaceful display of sovereignty.
Prescription is related to occupation, and refers to the acquisition of sovereignty by way of the actual exercise of sovereignty, maintained for a reasonable period of time, that is effected without objection from other states.
- Gilbert, Jérémie (2006). Indigenous Peoples' Land Rights Under International Law: From Victims to Actors. BRILL. p. 32. ISBN 9781571053695.