The Cold War is categorised as a state of prolonged military and political tension, primarily between the US and the Soviet Union, but it also included allies on both sides, known as the Western and Eastern Bloc countries. The tension began after WWII with the division of Germany and Berlin and centred around large political and economic differences between the two sides.
The Soviet Union sought to influence the governments and people of other countries in order to introduce its own political philosophy and the US attempted to stop the spread of Communism by doing the same. Although the two superpowers never engaged in direct combat with each other, they did play parts in several major conflicts and prepare for nuclear war with an arms race. The Cold War ended with the dissolution of the Soviet Union in 1991.