There are three main reasons why the Cold War ended. They include:
Inefficiency of the communist economy. The communist economy was not able to fulfill the material desires of its people. This, along with the political repressiveness of the system, made people in the communist bloc unhappy with communism.
Pressure from the US. The US put pressure on the USSR through an arms buildup under President Reagan. This forced the Soviets to use more resources for military purposes and fewer for consumer goods.
Gorbachev’s reforms. These reforms “opened the door” by giving Russians and others the idea that change could occur and their lives could be improved. Once Gorbachev opened the door, others, frustrated by the system they lived in, knocked the door down and ended communist rule.