Italy was a leading member of the Axis powers in World War II, battling on several fronts with initial success. However, after the German-Italian defeat in Africa and the Soviet Union and the subsequent Allied landings in Sicily, King Victor Emmanuel III overthrew and arrested Mussolini, and the Fascist Party in areas (south of Rome) controlled by the Allied invaders was shut down. The new government signed an armistice with the Allies in September 1943. Nazi Germany, with Fascists' help, seized control of the northern half of Italy and freed Mussolini, setting up the Italian Social Republic, a collaborationist puppet state still led by Mussolini and his Fascist loyalists. Italian resistance to Nazi German occupation and Italian Fascist collaborators manifested in the Four days of Naples, while the Allies organized some Italian troops in the south into the Italian Co-belligerent Army, which fought alongside the Allies for the rest of the war. A smaller number of Italian troops, still loyal to Mussolini and his RSI, continued to fight alongside the Germans in the National Republican Army. From this point on, the country descended in civil war, and a large Italian resistance movement fought a guerrilla war against the German and RSI forces. Mussolini was captured and killed on 28 April 1945 by the Italian resistance, and hostilities ended the next day.