ANNEXATION. — In the broad sense, this designates any non-natural enlargement of a State’s territory, however effected; but the term is more commonly used in the narrower sense of the incorporation into its own territory, by one State, of all or part of the territory of another State. A subspecies of a. in this second sense is “incorporation,” or the “total a.” of one State by another. In international practice, especially when the term is used in the broader sense, a. denotes the fact of territorial enlargement, as distinct from the unilateral or bilateral legal act from which the acquisition of sovereignty over the new territory derives: 1) occupation of nullus territory; 2) conquest; 3) debellatio; 4) cession; 5) adjudication. It is customary to distinguish from this figure the merger, which consists, according to prevailing opinion, in the formation of a new State through the voluntary extinction of pre-existing States. Relatively recent a. are those carried out by France during the Revolution and the Napoleonic period; those that marked the stages in the formation of the unified Italian State; the Prussian a. of 1866; the a. of the Boer State by Great Britain in 1902; of the Congo by Belgium in 1907; of Korea by Japan in 1910; the a. of Ethiopia to Italy in 1935; the a. of Austria to Germany in 1938; of eastern Poland (1939), the Baltic States (1940), and other territories to the USSR; etc. In constitutional practice and doctrine, a. is spoken of only with reference to territories that become an integral part of the metropolitan territory.
In addition to affecting territorial sovereignty, a. has varying effects, and effects of varying extent, on relations of subjection; on the ownership of the active and passive international legal relations that had belonged to the extinguished or dispossessed State; and on the constitutional, administrative, criminal, civil, and judicial organization of the annexed territory.