In 1939, however, news of the non-aggression pact between Nazi Germany and the Soviet Union forced Nizan to abandon the French Communist Party. Given his active participation in the anti-fascist movement, as well as his commitment to the republican cause of the Spanish Civil War, Nizan could not accept the party's rapid shift against the popular front. Soon thereafter, Nizan enlisted to fight in the French army with the onset of World War II, and was killed in the Battle of Dunkirk while part of the French rearguard protecting the British evacuation.