In politics, a defector is a person who gives up allegiance to one state in exchange for allegiance to another, in a way which is considered illegitimate by the first state. More broadly, it involves abandoning a person, cause or doctrine to which one is bound by some tie, as of allegiance or duty.
This term is also applied, often pejoratively, to anyone who switches loyalty to another religion, sports team, political party, or other rival faction. In that sense, the defector is often considered a traitor by their original side.
The physical act of defection is usually in a manner which violates the laws of the nation or political entity from which the person is seeking to depart. By contrast, mere changes in citizenship, or working with allied militia, usually do not violate any law.
For example, in the 1950s, East Germans were increasingly prohibited from traveling to the western Federal Republic of Germany where they were automatically regarded as citizens according to Exclusive mandate. The Berlin Wall and fortifications along the Inner German border were erected by the Communist East German Democratic Republic in 1961 to enforce the policy. When people tried to "defect" from the GDR they were to be shot on sight. Several hundred people were killed along the border in their Republikflucht attempt. Official crossings did exist, but permissions to leave temporarily or permanently were seldom granted. On the other hand, the GDR citizenship of some "inconvenient" East Germans was revoked, and they had to leave their home on short notice against their will. Others, like singer Wolf Biermann, were prohibited from returning to the GDR.