<P> All those aggressive moves met only feeble and ineffectual policies of appeasement from the League of Nations and the Entente Cordiale, in retrospect symbolized by British Prime Minister Neville Chamberlain's "peace for our time" speech following the Munich Conference (1938), that had allowed the annexation of the Sudeten from interwar Czechoslovakia . When in March 1939 the German Führer broke the promise he had made at that conference to respect that Czechoslovalia's future territorial integrity, sending troops into Prague, its capital, breaking off Slovakia as a German client - state, and absorbing the rest of the Czech lands as the "Protectorate of Bohemia - Moravia", Britain and France tried to switch to a policy of deterrence . </P> <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>

What was the cause of world war two