End of the Cold War.
Ronald Reagan would be the president who would start leading the US and the world for that matter out of the cold war. In 1989 he gave a speech in Berlin with the famous quote "Tear down that wall!" This speech was addressed to West Berlin and Mikhail Gorbachev who would be the last General Secretary of the Soviet Union. This single quote is the most memorable thing of Ronald Reagan's presidency.
For decades the Berlin wall had stood as the stark symbol between Communism and Capitalism. Soon after Ronald Reagan's speech the USSR gave permission for the wall to be torn down. By 1991 the Soviet Union ceased to exist and is now known today as the Russian Federation.
Before the fall of the Soviet Union Gorbachev knew the Soviet economy was in shambles after nearly 70 years of being a communist country. Gorbachev had the idea of Glasnost where the USSR would become more open to foreign goods and trade which would promote the economy. He also had the idea of Perestroika where citizens could have a share in the economy similar to stocks. By the end of the Cold War the US had spent trillions of dollars for a conflict that never came and lost thousands of lives in proxy wars that gave no benefit to the country.