annexation

n. addition, appending, attachment; territorial extension; connection, union

Annexation (Latin ad, to, and nexus, joining) is the legal incorporation of some territory into another geo-political entity (either adjacent or non-contiguous). Usually, it is implied that the territory and population being annexed is the smaller, more peripheral or weaker of the two merging entities. It can also imply a certain measure of coercion, expansionism or unilateralism on the part of the stronger of the merging entities. Because of this, more positive words like political union or reunification are sometimes preferred.
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Noun
1. incorporation by joining or uniting
(synonym) appropriation
(hypernym) incorporation
2. the formal act of acquiring something (especially territory) by conquest or occupation; "the French annexation of Madagascar as a colony in 1896"; "a protectorate has frequently been a first step to annexation"
(hypernym) acquisition

n. annexation, territorial extension, connection

(v. t.)
The union of property with a freehold so as to become a fixture. Bouvier. (b) (Scots Law) The appropriation of lands or rents to the crown.
  

(v. t.)
The act of annexing; process of attaching, adding, or appending; the act of connecting; union; as, the annexation of Texas to the United States, or of chattels to the freehold.