The statement that best describes the relationship that European communists and socialists had with their capitalist governments during World War II is:
European communists and socialists set up uneasy alliances with capitalists to defeat fascist and Nazi forces.
During the war, many communist and socialist groups formed alliances with capitalist governments, primarily due to the shared goal of defeating fascism and Nazism, despite their ideological differences. This alliance was often marked by tension and distrust but was deemed necessary to confront the greater threat posed by the Axis powers.