hi! FYI, it might be worth x-posting this question to /r/AskSocialScience

The easy narrative to understand is the war of purely political forces between Reagan and Mikhail Gorbachev. Contrary to political rhetoric today, Reagan was admired by Americans of a large spectrum of political ideologies, not just extreme right wingers. Reagan had a grandfather-like appeal, but he lacked extensive education. During the Cold War, Reagan actually studied Russian history and realized that things such as secret police and corrupt leadership were not explicitly communist functions, but elements of Russian history. Reagan then realized that by supporting Gorbachev's policy of glasnost (openness), the desire to end communism would emerge from the USSR itself.

However, a greater reason for why communism failed may be solely due to economic reasons. A market economy (capitalism) listens to the demands of consumers to produce the amount of goods desired by consumers, while command economies (socialist or communist economies) rely on government technocrats dictating how much of each good will be made. Market economies incentivize economic growth, whereas communist economies do not. Once the arms war began, communism really was destined to fail, as it could never create as much wealth as its capitalist competitors.

Consider North Korea and South Korea. They have nearly the same geography, natural resources, ethnic makeup, and historical background. One is a command economy, and the other is a market economy. Which would you consider the successful economy?