During the German invasion of Yugoslavia in 1941, these tensions grew to become one of the most brutal civil wars that occurred in World War II. The Royal Government soon capitulated, and the resistance was mainly made by the Četniks, who defended the restoration of the Monarchy, and the Partisans, who supported the creation of a communist Yugoslav state. The Serbs were divided into these two factions, that fought not only Nazi Germany and all the other neighbour Axis allied countries which also invaded different territories of Yugoslavia — the Italians, Hungarians and Bulgarians — but also each other. Beside this, other Yugoslav non-Serb nationalists took advantage of the situation and allied themselves with the Axis countries, regarding this moment as their historical opportunity of fulfilling their own irredentist aspirations, the Independent State of Croatia being by far the most brutal one.