<P> As Nazi attentions turned towards resolving the "Polish Corridor Question" during the summer of 1939, Britain and France committed themselves to alliance with Poland, threatening Germany with a two - front war . On their side, the Germans assured themselves of the support of the USSR by signing a non-aggression pact with Moscow in August 1939, secretly dividing Eastern Europe into Nazi and Soviet spheres of influence . </P> <P> The stage was then set for the Danzig crisis to become the immediate trigger of the war in Europe started on 1 September 1939 . Following the Fall of France in June 1940, the Vichy regime signed an armistice, which tempted the Empire of Japan to join the Axis powers and invade French Indochina to improve their military situation in their war with China . This provoked the then neutral United States to respond with a trade embargo . The Japanese leadership, whose aim was the Japanese domination of the Asia - Pacific, thought they had no option but to pre-emptively strike at the US Pacific fleet, which they did by attacking Pearl Harbor on 7 December 1941 . </P> <P> Meanwhile the Axis in Europe had brought the Soviet Union into the world war as an active belligerent by attacking eastwards in Operation Barbarossa (June 1941). </P> <P> The internationalist - minded, radical Bolsheviks seized power in Russia in November 1917, with the goal of overthrowing capitalism across the world . They supported communist parties in many countries and helped set up similar regimes in Hungary and Bavaria, Azerbaijan, Armenia and Georgia . By 1920 there was a corridor of anti-communist border states just west of Russia . However, these states feuded among themselves, and such alliances they formed, like the Little Entente, were unstable . </P>

What were the reasons of second world war