collaborationism is cooperation with the enemy against one's country of citizenship in wartime. the term is most often used to describe the cooperation of civilians with the occupying axis powers, especially nazi germany, fascist italy, and imperial japan, during world war ii. motivations for collaboration by citizens and organizations included nationalism, ethnic hatred, anti-communism, antisemitism, opportunism, self-defense, or often a combination of these factors. some collaborators in world war ii committed war crimes, crimes against humanity, or atrocities such as the holocaust. more often collaborators simply "went along to get along," attempting to benefit from the occupation or simply survive. the definition of collaborationism is imprecise and subject to interpretation.
stanley hoffmann subdivided collaboration into involuntary (reluctant recognition of necessity) and voluntary (an attempt to exploit necessity). according to him, collaborationism can be either servile or ideological. servile is service to an enemy based on necessity for personal survival or comfort, whereas ideological is advocacy for cooperation with an enemy power.  in contrast, bertram gordon used the terms "collaborator" and "collaborationist" for non-ideological and ideological collaborations, respectively. james mace ward has asserted that, while collaboration is often equated with treason, there was "legitimate collaboration" between civilian internees (mostly americans) in the philippines and their japanese captors for mutual benefit and to enhance the possibilities of the internees to survive. collaboration with the axis powers in europe and asia existed in varying degrees in all the occupied countries. although the united kingdom and the united states were never occupied, a british dependency, the channel islands near france, was under german occupation and thousands of american civilians in asia were interned by japan.
with the defeat of the axis, collaborators were often punished by public humiliation, imprisonment, and execution. in france, 10,500 collaborators are estimated to have been executed, some after legal proceedings, others extra-judiciously.
the opposite of collaborationism in world war ii was "resistance", a term which also has a broad range of meaning and interpretations.