He argued that Poland's border could then move westwards into Germany. Churchill and Roosevelt both disapproved. Churchill Knew that not much could be done, as the red army was in control of Poland and east Germany. He convinced Roosevelt to appease Stalin as long as Stalin did not interfere in Greece. .
The Yalta conference took place in February 1945 and is often thought as the height of wartime unity. The USSR agreed to join the war against Japan after the defeat of Germany, it was agreed Germany would be split into four zones and that war criminals would be hunted down. The basic structure of the UN was also agreed. .
After Yalta the USSR tightened its grip on Eastern Europe, seen by the West as aggressive and expansionist and by the soviets as simply maintaining security of the USSR. On 12th April 1945 Roosevelt died, replaced by the vice president Harry Truman, a bitter anti-Communist. He was much more suspicious of Stalin than Roosevelt. When Germany surrendered American troops began to move to the Pacific and Soviet superiority in Europe was overwhelming. However the USA tested the first atom bomb successfully on 16th July 1945, Truman's confidence grew with Stalin's fears. .
As previously mentioned the Red Army swept through Eastern Europe leaving in its wake pro-Moscow governments. As 1945 progressed this continued even more rapidly and the communist movements in Eastern Europe became stronger. Stalin made sure that he had a tight grip on Eastern Europe by introducing the Cominform, a body that coordinated all of the communist governments of Eastern Europe, keeping a close eye on each leader. .
The West could not simply allow this to happen they had to respond. Indeed the West did respond, the USA, the superpower of the West had traditionally favored a policy of isolationism. However a major turning point came when the USA committed itself to a policy of anti-communisms, they would prevent communism from spreading any further, and attempt to bring countries onto the capitalist side.