Annexation is an activity in which two things are joined together, usually with a subordinate or lesser thing being attached to a larger thing. In strict legal terms, annexation simply involves a consolidation or joining, but many people use the term specifically to discuss the annexation of territories by nations which feel that they have a claim on them. A number of nations expanded their political power through annexation historically, although the United Nations no longer recognizes annexation as a legitimate political tool.
In a legal sense, when something is annexed, it is appended or added to something else. For example, someone might annex a will by adding a codicil which changes the terms, or annex personal property by attaching it legally to a piece of real estate. Annexation in the legal community does not carry the same implications that others forms of annexation do.
Within a nation, incorporated entities can choose to annex neighboring land. This decision is usually made when a settled area wants to expand, or when it is already offering services to people outside its boundaries, and it wants to create a more formal arrangement. Usually, annexation is only allowed if the residents of the land being annexed vote to support it on a ballot, and annexation is sometimes opposed because people fear higher tax rates and other issues which may crop up when land is annexed by a larger neighboring city.
In the international community, annexation involves a nation laying claim to a territory and declaring that the territory is now part of the annexing nation. For example, the United States annexed Hawaii in 1898 with the goal of expanding control in the Pacific. These types of annexations often take the form of a takeover, in which a larger and more powerful state exerts control over a smaller territory or nation, effectively forcing it to join. Some people refer to this activity as a grab for land or power, as it is usually done with the goal of benefiting the nation doing the annexing.
After the Second World War, the United Nations passed a resolution condemning annexing, and stating that future annexations of territory would not be recognized by the international community, thereby invalidating them. This was done in part as a reaction to the annexations utilized by Germany to gain control over continental Europe during the war. A handful of annexations have occurred since this period, usually in a legal gray area which makes it difficult to categorically determine that they should be classified as annexations.