The leaders of the Soviet Union believed they were encircled on all sides by hostile capitalist powers. They feared a similar invasion to the one that had taken place during World War II with Hitler's Operation Barbarossa. This inculcated an attitude of general paranoia among the Soviet leadership, who believed that the USSR was involved in a life and death struggle with capitalism for world supremacy.

According to Marxist-Leninist ideology, capitalism would eventually be replaced by Communism, and the Soviet leadership sought to make that happen by spreading Communist ideas right across the globe, especially in the developing world. This was a way of taking the fight to the United States, which was the dominant world power.

Europe became a battle ground between the superpowers' ideologies. Countries such as France and Italy had large, well-organized Communist parties, which had attracted mass support due to the part they'd played in partizan warfare. The Soviets sought to exploit such popularity and use these parties to gain a foothold in Western Europe. The Truman Administration had other ideas, however, and under the Marshall Plan devoted vast resources to helping the shattered economies of Western Europe get back on their feet, thus making it more difficult for Communist parties to exploit widespread poverty and misery to obtain political power.

The United States, recognizing that direct conflict with another nuclear power would mean the end of the world, tried instead to contain the spread of Communism beyond its Eastern European stronghold. As well as economic measures, such as the Marshall Plan, as we've already seen, the United States funded, armed, and offered political support to a number of unsavory regimes that could be relied upon to crack down on the merest hint of Communist ideology in their respective territories.

The Truman Doctrine may have sparked the Cold War and heightened the tensions between the United States and the Soviet Union. In the United States, the Truman Doctrine stated that it would help countries threatened by the Soviet Union and the spread of communism. The United States demonstrated its intentions by aiding the anti-communist party during the Greek Civil War.

The Soviet Union stamped its authority on the Eastern Bloc and looked to expand its communist agenda to the rest of the world. The situation culminated in stiff competition with the United States, with each side trying to win over the different countries to their ideology.

Winston Churchill delivered the “Iron Curtain” speech calling for an alliance with the United States against the Soviet Union. Britain saw the U.S.S.R as a major threat, especially with regard to the control of Europe. The situation saw an alliance between France, Britain, and the United States (among other western allies), which formed the Western Bloc to oppose the Soviet Union’s Eastern Bloc.

In the Soviet Union, the Cold War developed out of a deep distrust of the United States and Great Britain that only became worse in the aftermath of World War II. In particular, it emerged from fears that the United States was extending its influence into Europe to an alarming degree, possibly even blocking Soviet plans to ensure a barrier of satellite states between the USSR and the West. 

In the United States, on the other hand, the fear was that Stalin would expand Soviet influence westward into Western Europe, which would deny the Americans crucial allies and trading partners. US fears were exacerbated when communist armies seized control of China after a long and brutal struggle. The United States became committed to resisting the spread of communism, a policy that became known as containment.

Europe became the earliest "battleground" of sorts in the Cold War, as the United States and the USSR vied for influence in many of the nations most devastated by the conflict, where society and government was the least stable. The conflict between the two superpowers (a new term coined during the Cold War) left Europe divided, east from west, a situation which was most marked in Germany and elsewhere along the borders of the so-called "Iron Curtain."