After the German invasion of Greece, in 1941 the Nazi Germans transferred him to the Dachau concentration camp, from where he was released in May 1945. Returning to Greece, he re-assumed the leadership of the KKE from Georgios Siantos, acting general secretary of the KKE since January 1942. The bloody Dekemvriana event had just ended with communist defeat. Zachariadis now declared his political intention for the KKE to fight for democracy and the people's power through elections.