In 1979, the Soviet Union invaded Afghanistan to try propping up the communist government there, which was being attacked by Muslim Mujaheddin fighters. This immediately caused a rift with America, which boycotted the 1980 Olympics.
In 1980, Ronald Reagan became president of the USA. As a strong anti-communist, he called the Soviet Union the 'evil empire' and increased spending on arms. The US military developed the neutron bomb, cruise missiles and a "Star Wars" defence system using space satellites.
By 1985, the Soviet Union was in trouble. In 1985, Mikhail Gorbachev became leader of the USSR.
As in 1956 and 1968, a relaxation by the Soviet government encouraged revolutions in Eastern Europe, only this time, the USSR did not have the means or the will to impose military control.