The cold war erupted in 1945 for various reasons. To a large extent of hostility arose from the American's side, as well as from the Soviet's side. There were many things that occurred during 1945-1948, from the first conflicts between Russia and the U.S. in Iran to the Berlin Blockade in 1948. As well as past conflicts contributed to the Cold War. And as time passed, more and more tension grew between the two nations. From past conflicts to apposing worldviews, tension grew.
One of the first things that sparked tension between the U.S. and Russia was the conflicts between Russia and the U.S. in Iran. For six months after the war, there was to be no foreign troops in Iran. However, the Soviet did not remove their troops. What's even worse the Soviets decided while they"re there, why don't the help spread communism in Azerbaijan. I ran also began to take over parts of northern Iran. This began to spark a little tension out of the Americans and the British, for they feared that if not acted upon sooner, the entire country would have been taken. Therefore the British and the Americans decided to put some pressure upon the Soviets and push them from Iran.
Another problem during 1946 was the intrusion of the eastern Mediterranean. America saw the threat when Stalin decided to send 25 Soviet divisions into Turkey. SO America decided to flex her arms and really show how powerful the U.S. is by showing off their nuclear weapons. That did the trick, and before you know it the Soviets went into submission.
As the Soviet power began to take more and more in Western Europe, The Americans were getting more and more nervous. They Americans knew that the economy of Western Europe was at a low, and was not equipped enough to defend them against Russia. So the Americans decided to do something about it, they produced the Marshall Plan. This gave economic help to nations outside of the Soviet control.