The origins of the Cold War actually start during WWII. During the war against Germany, Stalin's armies suffered massive casualties as they pushed Hitler's army out of the Soviet Union and across Eastern Europe. Stalin did not allow for the Baltic Republics, Poland, or Hungary to be ruled by self-determination; rather, he set up puppet states that would be friendly to the Soviet Union. Stalin did not trust the Western governments after WWII, especially Britain. Stalin thus sought to create a buffer zone of influence around the Soviet Union. When Truman protested this sphere of influence, Stalin claimed that the United States enjoyed the same thing through the Monroe Doctrine. Stalin also increased the number of purges of intellectuals and army officers after WWII and he even detained former Soviet prisoners of war because he was worried that Germany indoctrinated them. Stalin spent money to encourage states such as Italy and Greece to vote for Communist leaders and he even funded Communist guerrillas in Greece to overthrow the democratically elected government. Stalin encouraged the development of the atomic bomb through the use of Soviet espionage efforts in America and captured German scientists after the fall of Berlin. Stalin blockaded Berlin in order to make the Western powers leave their part of the occupied zone--this led to the American-led Berlin airlift. Stalin was not friendly with the West after WWII, since he saw the West as an adversary. Stalin stopped short of going into "hot" war with the West, primarily because his industries and armies suffered so extensively during WWII.