 Complete the following phrase:  On 23 August 1939, after unsuccessful efforts to form an anti-fascist alliance with Western powers, the Soviets signed the non-aggression agreement with Nazi Germany. After the start of World War II, the formally neutral Soviets invaded and annexed territories of several Eastern European states, including eastern Poland and the Baltic states. In June 1941 the Germans invaded, opening the largest and bloodiest theater of war in history. Soviet war casualties accounted for the majority of Allied casualties of the conflict in the process of acquiring the upper hand over Axis forces at intense battles such as Stalingrad. Soviet forces eventually 