Collaboration
Collaboration is collaboration with a (foreign) enemy in which one turns against one's own people and government.
Collaborators were considered disloyal to the nation and thus to be committing treason. In the case of the German occupation of the Netherlands during World War II, a number of groups are considered collaborators. For example, NSB members, people working for the Sicherheitsdienst, companies that were gaining economic advantage and people who signed up for the Waffen-SS.