The alliance between Great Britain, The United States and USSR ended just after World War II, when the U.S. decided to drop an atomic bomb on Japan, and the USSR felt that America had secretly developed the atomic bomb. A rivalry started to grow between communist and non-communist countries which led to the Cold War. After World War II ended Germany was split into four parts, as well as its capital Berlin. The beginning of the Cold War was marked by Germans unwilling to re-unite. By 1948, Russia controlled much of Eastern Europe, including East Germany and East Berlin, while the United States, Great Britain and France controlled Western Europe along with West Germany and West Berlin. The division of Europe was referred to as the Iron Curtain. The Truman Doctrine in 1947 enabled America to help any non-communist country to resist communist countries; in other words, the United States employed a policy of containment against communists and the USSR, meaning that its tactic was to prevent the spread of communism by restricting communism to within its borders. One phase of containment was the Marshall Plan, which stated that America would give economic assistance to countries recovering from World War II. This would prevent another depression, and terminate the possibility of allied countries adopting a communist government. All countries that were offered the money accepted it, except for the USSR, which declared that it would signify American dominance. Another phase of containment was the United States starting the North Atlantic Treaty Organization (NATO), which unified the western countries against an attack from the USSR. The USSR responded with a blockade around West Berlin, which was located deep inside eastern territory. All food and supplies had to be airlifted to West Berlin until May 1949.
The clashing of communism and capitalism was the most direct cause of the Cold War. The creation of the atomic bomb in 1945 by the United States and its later use on Japan intensified the rivalry as the USSR was now worried about their safety. By placing spies in theAmerican government, they were able to create their own arsenal of atomic weapons. When America created the hydrogen bomb in 1952, the USSR created its own in 1955. Then, on October 4, 1957, the Soviets launched Sputnik into space. As the nuclear weapons race evolved into a race-to-space, the Soviets launched Sputnik II with a dog named Laika, which was the first living creature in space. It wasn't until January 31, 1958, when America launched its first satellite, the Explorer I, into orbit.
Even more tension was added to the Cold War when, in 1961, Germany built the Berlin Wall. The open border was allowing East Europeans to escape Soviet rule through West Berlin. This was a major political embarrassment and had tremendous effects on the Soviet economy. The Berlin Wall wasn't torn down until October 3, 1990.
As communist Cuba thought that the U.S. was planning an attack against them, they asked the Soviet Union for help. The Soviet Union sent them materials to build anything they needed to launch their own missiles. When America found out the Cuba could possibly launch missiles into America, we ordered that the Soviets pull out all of their nuclear equipment. Although Cuban leader Fidel Castro protested this, the Soviets withdrew, and one of the biggest early potential Cold War disasters had been averted.