Annexation (Latin ad, to, and nexus, joining) is the administrative action and concept in international law relating to the forcible acquisition of one state's territory by another state and is generally held to be an illegal act. It is distinct from conquest, which refers to the acquisition of control over a territory involving a change of sovereignty, and differs from cession, in which territory is given or sold through treaty, since annexation is a unilateral act where territory is seized and held by one state. It usually follows military occupation of a territory.
This article is missing information about annexation of unclaimed territory and territories requesting annexation, e.g. the annexation of Texas by the United States. (December 2020)