In the second World War the Soviet Union and U.S. were allies.After the second World War only the two most powerful countries U.S. and Soviet Union remained strong. The two countries became nervous that the other country was going to attack their country. That is how their alliance broke. Mikhail Gorbachev wanted to stop the Cold War. In the Cold War the two countries showed their military power and using their ideas they wanted to control the world.Gorbachev reduced the military spending because they were using to much to build weapons and the country was poor. Gorbachev started to help the country using Glasnost and Perestroika.The U.S. also reduced their military spending by 50%. Then the USSR started to collapse. After that, the USSR no longer existed. Finally, the Cold War ended.