Wartime collaboration is cooperation with the enemy against one's country of citizenship in wartime.[1] As historian Gerhard Hirschfeld says, it "is as old as war and the occupation of foreign territory".[2]
The term collaborator dates to the 19th century and was used in France during the Napoleonic Wars. The meaning shifted during World War II to designate traitorous collaboration with the enemy. The related term collaborationism is used by historians who restrict the term to a subset of ideological collaborators in Vichy France who actively promoted German victory.
Hirschfeld-1989 was invoked but never defined (see the help page).