Acquisition of sovereignty

A number of methods of acquisition of sovereignty are or have been recognised by international law as lawful methods by which a state may acquire sovereignty over .

Accretion refers to the physical expansion of an existing territory through geographical processes, such as alluvion (the deposit of sediment) or vulcanism.

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.

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