The Cold War was a post 1945 struggle between the United States and its allies and the group of nations led by the Soviet Union. There was never a direct military conflict but there were economic and diplomatic struggles between the two superpowers.
The USA and the Soviet Union became enemies in 1917 when the Communists seized power and established the Soviet Union. In 1946 U.S. officals interpreted a speech by Stalin as declaring a war against the West.
In 1961 the USSR tried to protect Communist East Germany with the Berlin Wall. The two superpowers attempted to gain influence in nations all over the world, in Asia, Africa, the Middle East and Latin America.
In 1985 Mikhail Gorbachev and Ronald Reagan agreed to end the arms race and the Cold War.
The Cold War finally ended in Europe when the East European nations elected non- Communist goverments and the two Germanies became one.