Cold War existed between the United States and Soviet because of political and economic differences leading to various conflicts around the world.
Cold War began in 1947 because US and Soviet Union had opposite beliefs. Soviet Union dominated Eastern Europe and the US believed in the containment of communism as the believed in Capitalism and Democracy, free elections and Soviet wanted total dictatorship
The containment policy made by the U.S. was to stop the further expansion of the USSR and the spread of Communism. The U.S. needed to contain and isolate Communism so it wouldn't spread to other countries. George F. Kennan was the first to introduce this policy in 1947. This was considered the start of the Cold War.
On August 29th, 1949, the Soviet Union detonated its first atomic bomb.This begins the competition between the U.S. and Soviet Union to expand their stock pile of weapons in order to gain superiority
Some of the events emerged during the Cold War was the formation of NATO happened in 1949 after a series of events that furthered the expansion of Communism. In total 12 countries signed the North Atlantic Treaty Organization that basically said if a country not in NATO attacked one country in NATO with its military it will be considered an attack against them all. This still exists today.
Other was that US developed Berlin Airlift to help West Berlin, The Berlin Airlift was a response to the USSR stopping land routes into Berlin. The U.S. had to bring food, water, and supplies to people living in the city by air. The blockage that caused the airlift was to try and get the capitalists out of Berlin but it had failed.