In June 1987, President Reagan came to the Berlin Wall and make a famous appeal to Soviet Communist Party leader Mikhail Gorbachev: "Mr. Gorbachev, tear down this wall."
The Western world applauded. But without Gorbachev, historians said the wall might not have come down in November 1989.
Gorbachev came to power in the Soviet Union in 1985, the first Soviet leader to have been born after the 1917 revolution that ended the Russian empire. The USSR was at a standstill: a stagnant economy, an inefficient bureaucracy, a disgruntled population and an outdated political system with entrenched bureaucrats.
He immediately saw the need for reform and in the coming years would institute several that would restructure the government and give the Soviet people freedoms they had long been denied.
"That was the signal, that was the starting point," said Irina Kobrinskaya, a research fellow at the Institute for World Economy and International Relations in Moscow. "He decided it's high time to tell [the] truth, to be critical."
In January 1987, Gorbachev called for multi-candidate elections by secret ballot, something the Soviet Union had not seen. The new rules would transform the Soviet parliament elections of March 1989, when many of the most powerful communist leaders were voted out.
"We initiated [the reforms] because they were overdue," Gorbachev wrote in a recent New York Times editorial. "We were responding to the demands of the people, who resented living without freedom, isolated from the rest of the world."
"In just a few years -- a very short time in history's span -- the main pillars of the totalitarian system in the Soviet Union were dismantled and the ground was readied for a democratic transition and economic reforms," he continued. "Having done that in our own country, we could not deny the same to our neighbors."
Reagan recognized early on that Gorbachev was a man he could work with. He stopped referring to the USSR as "the Evil Empire," and over a series of summits the relationship between Moscow and Washington thawed considerably.
Gorbachev gradually repealed the Brezhnev doctrine, the policy that Moscow used to involve itself in the affairs of the USSR's central European satellite countries. Gennadi Gerasimov, a Soviet official, would later jokingly describe Gorbachev's shift as the "Sinatra Doctrine" on ABC's Good Morning America in 1989.
"We now have the Frank Sinatra doctrine. He has a song, 'I Did It My Way.' So every country decides on its own road to take," said Gerasimov, a spokesman for the Soviet Foreign Ministry.
One by one, the countries of central Europe toppled their Soviet-controlled Communist governments -- Poland first, Hungary second. Germans on both sides of the Berlin Wall were stirring, calling for unification. When East German demonstrators demanded that they be let into West Germany on that fateful November 9, the Soviet Union did nothing to prevent it.
"If the Soviet Union did not want it, nothing would have happened, not any kind of unification," Gorbachev told reporters last week. "But what would have happened instead? I don't know, maybe a World War III."
"I am very proud of the decision we made," he said. "The wall did not simply fall, it was destroyed, just as the Soviet Union was destroyed."
Destroying the Soviet Union was not Gorbachev's intention. But as his reforms took hold, the results grew beyond his control.
Central European countries continued to rise up and declare independence: Czechoslovakia, Bulgaria, Romania, Albania and Yugoslavia.
East Germany was just one on the list but it dramatically captured the period's mood. "To put it briefly, the fall of the Berlin Wall was a synthesised indication of what was going on in the world and where it was heading to," Gorbachev said Thursday.
"It was very, very symbolic," says Kobrinskaya. "The Berlin Wall was a symbol of a bipolar world of two systems which co-existed and confronted."
Over the next two years, a wave of self-determination swept over the Soviet Union. Its 15 republics were increasingly free to set their own course -- and break away from Moscow. The USSR continued to unravel as Gorbachev struggled to walk a thin line between supporting reform while keeping the union intact.
In August 1991, almost two years after the Berlin Wall fell, communist hardliners arrested Gorbachev in an attempted coup d'état. After days of protests the coup ended and Gorbachev was restored to power.
By that point, the Soviet Union was unified in name only. Each republic declared its independence in the months that followed and on Christmas Day 1991, Gorbachev resigned and the USSR ceased to exist.
Gorbachev won the Nobel Peace Prize in 1990 for helping to bring the Cold War to a close. A hero to many in the West, Gorbachev keeps a low profile in Russia where many still mourn the breakup of the Soviet Union.
"My policy was open and sincere, a policy aimed at using democracy and not spilling blood," he said last week. "But this cost me very [dearly], I can tell you that."