From The Art and Popular Culture Encyclopedia
Since World War II the term "collaboration" acquired a negative meaning as referring to persons and groups which help a foreign occupier of their country—due to actual use by people in European countries who worked with and for the Nazi German occupiers. Linguistically, "collaboration" implies more or less equal partners who work together—which was the meaning the Nazi German occupiers were suggesting for ideological reasons but was obviously not the case as one party was an army of occupation and the other were people of the occupied country living under the power of this army. Thus, the term "collaboration" acquired during World War II the additional sense of criminal deeds in the service of the occupying power, including complicity with the occupying power in murder, persecutions, pillage, and economic exploitation as well as participation in a puppet government.
The use of "collaboration" to mean "traitorous cooperation with the enemy," dates from 1940, originally in reference to the Vichy Regime in France, the French civilians who sympathised with Nazi Germany's doctrine, and voluntary troops (LVF) who fought against the Free French and later De Gaulle's French Force. Since then, the words collaboration and collaborateur may have this very pejorative meaning in French (and the abbreviation collabo has only this pejorative and insulting meaning). Nonetheless, collaboration and collaborateur have kept in French their original positive acceptations –with, for example, collaborateur still commonly used in referring to co-workers.
In order to make a distinction, the more specific term Collaborationism is often used for this phenomenon of collaboration with an occupying army. However, there is no water-tight distinction; "Collaboration" and "Collaborator", as well as "Collaborationism" and "Collaborationist", are often used in this pejorative sense—and even more so, the equivalent terms in French and other languages spoken in countries which experienced direct Nazi occupation.