Annexation. — In a broad sense, the term denotes any unnatural increase in a State’s territory however effected, but it is more commonly used in the narrower sense of the incorporation into one’s own territory, in whole or in part, of the territory of another State. A subspecies of annexation in this second sense is the “incorporation” or “total annexation” of one State by another. In international practice, especially when the term is employed in the broader sense, annexation refers to the fact of territorial growth distinct from the unilateral or bilateral juridical act by which sovereignty over the new territory is acquired: (1) occupation of *terra nullius*; (2) conquest; (3) *debellatio*; (4) cession; (5) adjudication. From this figure is distinguished the merger, which, according to prevailing opinion, consists in the formation of a new State through the voluntary extinction of pre-existing States.
Relatively recent annexations include those effected by France during the Revolution and the Napoleonic period; those marking the stages in the formation of the unified Italian State; the Prussian annexations of 1866; the annexation of the Boer State by Britain in 1902; of the Congo by Belgium in 1907; of Korea by Japan in 1910; the annexation of Ethiopia by Italy in 1935; the annexation of Austria by Germany in 1938; of eastern Poland (1939), the Baltic States (1940), and other territories by the USSR; and so forth. In constitutional practice and doctrine, annexation is spoken of only with reference to territories that become integral parts of the metropolitan territory.
Beyond territorial sovereignty, annexation variably affects relations of subjection, the holding of active and passive international legal relations that had belonged to the extinguished or dispossessed State, and the constitutional, administrative, penal, civil, and judicial order of the annexed territory.