Even before 1939 there were old apprehensions between East and West. The West disliked communism and viewed it as a dishonest and despicable system, one, which was completely incompatible with capitalism. The Western powers supported the Anti-communists in the Russian Civil War proving that they wanted to fight against communism. The Nazi-Soviet Pact of August 1939 outraged the West, who thought that Stalin had gone behind their back and even though he had always said he hated Germany he had made a deal with them. More than anything else however the principles of the West and the East differed greatly and neither one felt they could trust the other. .
However WWII brought East and West together as the USSR, the USA and Britain fought together against Italy, Japan and Germany. The allies co-operated during the war, supplying each other with arms and attending conferences together, such as Yalta and Potsdam. The war had untied them; they all fought against a single evil. Even though they were wartime allies their old differences and mistrusts were not cured but simply suppressed. Stalin felt that the West had invaded Russia many times before and could not be trusted. It wanted to be protected. The West believed Russia wanted to expand communism and dominate Europe. The Soviets however believed that it needed protection from future invasions, and so the soviet sphere of influence was born. Communist governments sprouted all over Eastern Europe. During the last years of the Second World War, the Red Army was moving forward and leaving behind pro- communist governments. The West saw this as one occupying force being replaced by another whereas the Soviets thought that they were merely securing the security of the USSR. Also at the Yalta conference, the allies agreed that Eastern Europe should become a sphere of influence but still there was notorious disagreement over the ruling of Poland. Stalin wanted the Russian border to move west into Europe.