When World War II broke out in Germany and all over Europe, America and the Soviet Union put aside their differences to help put an end to Hitler's reign. In 1945, when the war had ended, tensions started to mount over many things, that had deep roots in ideology and history with the Soviet Union. There was a lot of political and economical influence to be made in a post war world, and both the United States and the Soviet Union wanted as much as they could get. In the post war world there were many disagreements that the United States had with the Soviet Union such as, the control of atomic weapons, the government in Poland and Iran. These events and others are eventually what led up to the mass weapons build up we know as the Cold War. .
When Europe was thrown into World War I in 1914, Tsar Nicholas II joined with the allies and declared war on Germany. After the Bolshevik Revolution of 1917 the new communist Soviet Union no longer had a struggle among imperialists, they then signed a separate peace with Germany and proclaimed their main goal, which was to overthrow world capitalism. Between World War I and II the US viewed the Soviets as a threat to US security and didn't grant diplomatic recognition to the Soviets until 1933. However, everything was put aside when World War II broke out.
President Roosevelt was still very cautious of the Soviet Union and hid Manhattan project from Stalin, until Stalin found out through espionage and began his own program for developing weapons. Churchill never doubted Stalin's duplicity and told Roosevelt to beware of Stalin. Stalin's wartime killing of thousands of Polish officers and blaming it on the Nazi's helped out Churchill's case on not trusting the Soviets. Other tensions were raised in World War II, for example when the Red Army was struggling with the Nazi armies of Germany, Stalin told his Allies in the West to open up a new front to take the heat off the Red Army and the United States and Great Britain waited until 1944, which increased Stalin's suspicions of Western democracies.
