I've answered a similar question before, which asked: "In what ways did Reagan deal with the Cold War?" I've copy-and-pasted it below.

Generally speaking, we can divide the Reagan administration into two distinct periods. The first, from Reagan's inauguration to late 1983-early 1984 was defined by bellicose rhetoric and aggressive actions against the Soviet Union. It was during this period that Reagan referred to the Soviet Union as an "evil empire" and claimed that Marxism-Leninism would end up on "the ashheap of history." Reagan backed up this confrontational rhetoric with action. In 1981, he instituted the largest peacetime military budget in U.S. history—roughly thirty percent of the entire federal budget. He additionally proposed the creation of a Strategic Defense Initiative (SDI) that would create a “nuclear umbrella” of spaced-based missile defense technology that could protect against any incoming Soviet missiles. It's difficult to overstate how much Gorbachev feared SDI, as he believed that the United States would actually use this technology, nominally for defense purposes, as an offensive weapon. As many critics said of SDI, Reagan was attempting to militarize outer space.

Reagan became even more aggressive in 1983. For instance, he approved the commencement of Able Archer, a military exercise meant to test the United States’ nuclear capabilities in the case of war against the Soviet Union. As a part of the exercise, the U.S. Pacific Fleet conducted its largest naval exercise in history right next to Soviet waters.

Tensions between the two superpowers neared a boiling point on September 1, 1983, when a Soviet fighter jet shot down Korean Air Lines flight 007, which had inadvertently crossed into Russian airspace. Two hundred and sixty-nine people died, including sixty-one U.S. citizens. By 1983, Reagan’s confrontational rhetoric and policies, in addition to the Korean Air Lines tragedy, heightened Cold War superpower tensions to their highest level since the Cuban Missile Crisis in 1962.

Reagan additionally heightened Cold War tensions through his support for various Third World insurgent groups that were fighting communist-supported governments, most notably in Afghanistan and Nicaragua. Reagan wanted Afghanistan in particular to be the Soviet Union's equivalent to the U.S.'s Vietnam War.

In 1984, however, Reagan began to radically shift his policy toward the Soviet Union. One historian refers to this shift as "the Reagan reversal," which occurred for several reasons: The administration was finally able to develop a coherent foreign policy agenda; U.S. allies in Europe were urging Reagan to tone down his aggressiveness; and, after 1983, Reagan became genuinely afraid that the United States and Soviet Union would go to war if they continued to be so confrontational.

Mikhail Gorbachev's rise to power in the Soviet Union was even more important than the Reagan Reversal. U.S. officials saw Gorbachev as a reformer, someone who they could work with to lessen or even end the Cold War. Because of that, Reagan purposefully took a less aggressive stance toward the Soviets in order to help Gorbachev avoid internal criticism from Politburo members who were advocating a hardline stance against the U.S. The last thing Reagan wanted was for aggressive U.S. actions to precipitate Gorbachev's ouster, and for him to be replaced with a less cooperative Soviet leader. In many ways, this policy of cooperation continued under George H.W. Bush, who avoided using triumphalist rhetoric as Eastern European countries began to break away from the Soviet Union. This was very important, and helped ensure that Gorbachev was able to stay in power throughout the turbulent period from 1989-1991

Reagan's role in ending the Cold War was less important than Gorbachev's reforms and vision. Gorbachev offered a completely different interpretation of American global ambitions than his Cold War predecessors. He didn't believe that capitalism was inherently expansionist or that the U.S. was attempting to surround the Soviet Union. As Melvyn Leffler has argued, this change in Soviet threat perception allowed Gorbachev to focus his attention on domestic matters, particularly his policies of glasnost and perestroika. Leffler gives Gorbachev the credit of being the “indispensable agent of change” that brought about the end of the Cold War. Reagan's role was still important, though. Most importantly, he recognized that Gorbachev genuinely wanted to end the Cold War.

While historians debate whether it was Gorbachev or the changing structure of the international order that brought about the end of the Cold War, most scholars agree that Reagan's foreign policy was only a secondary factor. This is not to discount Reagan's role in the end of the Cold War. There were many chances in which Reagan's actions might have actually prolonged the Cold War, particularly if he had continued to act aggressively and forced the Soviet government to go in and militarily repress the revolutions in Eastern Europe. No historian really says that Reagan did a bad job with his Cold War policy. He is generally seen as having skillfully recognized Gorbachev's sincerity and desire for cooperation. For this, Reagan deserves a lot of credit.

Some historians argue that Reagan knew what he was doing all along, that historians can't really divide the administration up into two distinct eras--one of conflict, one of cooperation. These historians are called "triumphalists." Hal Brands is one historian in this camp. He claims that Reagan's shift from confrontation to cooperation was done deliberately--kind of like a bad cop/good cop strategy where you make the enemy fear you, then offer to negotiate.

I don't, however, want to give too much emphasis to the triumphalist interpretation. Most scholars disagree with it. Many triumphalists are, perhaps unsurprisingly, Reagan officials: Jack Matlock, Robert Gates, Richard Pipes, and several others.

In contrast to the triumphalists, other historians, like Beth Fischer, argue that Reagan simply bungled his foreign policy during his first term, and was only able to get his act together by late 1984. In other words, there was no bad cop/good cop strategy. Reagan just didn't really know what he was doing for the first three or four years he was in office.

Whether triumphalist or not, almost all historians accept that from 1984 onward Reagan handled foreign policy with the Soviet Union incredibly well. Most, however, believe that Reagan's ultimate role was as an expediter rather than a primary cause for the Cold War's end.

Sources:

• Melvyn Leffler, For the Soul of Mankind: The United States, the Soviet Union, and the Cold War

• Hal Brands, What Good is Grand Strategy?: Power and Purpose in American Statecraft from Harry S. Truman to George W. Bush

• Campbell Craig and Fredrik Logevall, America's Cold War: The Politics of Insecurity

• Beth Fischer, The Reagan Reversal: Foreign Policy and the End of the Cold War

• John Lewis Gaddis, The Cold War: A New History