<P> South Africa was a sovereign Dominion under the South African monarchy, as per the Statue of Westminster 1931 . South Africa held authority over the mandate of South - West Africa . </P> <P> Yugoslavia entered the war on the Allied side after the invasion of Axis powers on 6 April 1941 . Royal Yugoslav Army was thoroughly defeated in less than two weeks and the country was occupied . The Italian - backed Croatian fascist leader Ante Pavelić declared the Independent State of Croatia before the invasion was over . King Peter II and much of the Yugoslavian government had left the country . In the United Kingdom, they joined numerous other governments in exile from Nazi - occupied Europe . Beginning with the uprising in Herzegovina in June 1941, there was continuous anti-Axis resistance in Yugoslavia until the end of the war . </P> <P> Before the end of 1941, the anti-Axis resistance movement split between the royalist Chetniks and the communist Yugoslav Partisans of Josip Broz Tito who fought both against each other during the war and against the occupying forces . The Yugoslav Partisans managed to put up considerable resistance to the Axis occupation, forming various liberated territories during the war . In August 1943, there were over 30 Axis divisions on the territory of Yugoslavia, not including the forces of the Croatian puppet state and other quisling formations . In 1944, the leading Allied powers persuaded Tito's Yugoslav Partisans and the royalist Yugoslav government led by Prime Minister Ivan Šubašić to sign the Treaty of Vis that created Democratic Federal Yugoslavia . </P> <P> The Partisans were a major Yugoslav resistance movement against the Axis occupation and partition of Yugoslavia . Initially the Partisans were in rivalry with the Chetniks over control of the resistance movement . However, the Partisans were recognized by both the Eastern and Western Allies as the primary resistance movement in 1943 . After that, their strength increased rapidly, from 100,000 at the beginning of 1943 to over 648,000 in September 1944 . In 1945 they were transformed into Yugoslav army, organized in 4 field armies with 800,000 fighters . </P>

What brought the usa into the war on the side of the allies