defection

thumb|A Soviet Lavochkin La-7 fighter aircraft that crash-landed in [[Sweden after being flown there by a defecting pilot, May 1949]]

In politics, a defector is a person who gives up allegiance to one state in exchange for allegiance to another, changing sides in a way which is considered illegitimate by the first state. More broadly, defection involves abandoning a person, cause, or doctrine to which one is bound by some tie, as of allegiance or duty.