Good Evening! I'll try to answer this to the best of my ability.

The Cold War is a really sticky subject to many historians, dating back to the Truman administration. Truman was an ardent anti-communist, and many of the policies that Roosevelt had agreed during his presidency, were no longer upheld.

So you fast forward to Reagan's administration, and he was preceded by President Carter. This is important, as during this administration the Carter Doctrine was passed. This essentially stated that the United States had the right to intervene any place on the globe in order to stop the aggression of the Soviets. Reagan continued these ideals, and rebranded them as the Reagan Doctrine. He believed that it was America's duty to protect democracy against the Society Union, and that low intensity conflicts would be used to win wars, instead of major battles.

There were several major events that occurred that help in the fall of the Soviet Union, as well as bring the Cold War to an end, but it wasn't completely Reagan that you have to look at. You have to realized that Gorbachev was the leader of the Soviet Union during this time period, and he was really progressive in the sense that he believed if you gave people freedom, that they would police themselves. So he started giving all of these freedoms to the people of the Soviet Union, and he put in to affect Glasnost (which essentially fought for a transparency within the leadership of the Soviet Union) and Perestroika (which meant that Gorbachev was fighting to restructure the economy as well as the political system). He allows a lot of countries that were formerly tied to the Soviet union, such as Hungary and Poland, to liberate themselves. He believed that the Soviet Union was on the brink of collapse, and that the economy was so bad because of Communism. He also replaced a lot of people within the Kremlin with younger, more educated men. He really wanted to turn the Soviet Union around in favor of the people, and even declared a "Peace Offensive" with the United States, trying to rebuild their relationship. Unfortunately, he encountered a lot of resistance from the Old Guard, and the people also began to resist after their was a scarcity of vodka, sugar, and ice cream.

Reagan became good friends with Gorbachev during this period, and was even pictured as walking around red square with him, after stating that the United States needs to stand firm against the Soviets. Reagan and Gorbachev began to have peace talks, and in the Summit of 1985, they agree to reduce the amount in their nuclear arsenal, and to eliminate the arms race. During this summit, they also agreed to open up a cultural exchange program. There was also the Strategic Arms Reduction Talks, which Reagan and Gorbachev met to really discuss the reduction of their nuclear stock piles, and how to dis arm and get rid of the materials, and what they should do with all of it afterwards. After all of this, Gorbachev appeals to Reagan, asking for help to turn the Soviet economy around, and he fails to get any support. The unemployment rate skyrockets throughout the Soviet Union, and he receives more resistance for the changes he was trying to make, eventually causing an internal collapse of the Soviet Union.

(This was my first response to this sub, I'd love to get some feedback, and to hear other people's opinions on this matter.)