Trace the diplomatic and internal Soviet developments that ended the Cold War between 1985 and 1991, and assess the conflict's legacy using more than one explanation.
Mikhail Gorbachev became the Soviet Union's leader in 1985 and, recognizing the Soviet economy and system were failing, introduced glasnost (political openness) and perestroika (economic restructuring) -- reforms meant to save the Soviet system that instead accelerated its unraveling by allowing open criticism the system had never permitted before. Reagan and Gorbachev met at a series of summits -- Geneva (1985), Reykjavik (1986), Washington (1987), and Moscow (1988) -- building a surprising personal rapport between two leaders who had each once cast the other's nation in the starkest terms; the 1987 INF Treaty eliminated an entire class of intermediate-range nuclear missiles, the first treaty to actually reduce, not merely limit the growth of, nuclear arsenals. Standing at Berlin's Brandenburg Gate in June 1987, Reagan directly challenged his counterpart: "Mr. Gorbachev, tear down this wall!"
Change came faster than almost anyone predicted. Poland's Solidarity movement, led by Lech Walesa, won the Eastern Bloc's first free elections in 1989; similar peaceful revolutions swept Hungary, East Germany, and Czechoslovakia's "Velvet Revolution" within months, as Gorbachev, unlike his predecessors, declined to use Soviet military force to prop up these communist governments. The Berlin Wall itself fell on November 9, 1989, as East German crowds simply began crossing and dismantling it; Germany formally reunified in October 1990. Inside the USSR, a hardline coup attempt against Gorbachev failed in August 1991 but fatally weakened his authority and accelerated the union's collapse; the Soviet Union formally dissolved on December 25-26, 1991, splitting into fifteen independent nations, with Boris Yeltsin emerging as Russia's new president. Separately, when Iraq invaded Kuwait in August 1990, a U.S.-led coalition authorized by the United Nations -- a level of great-power cooperation impossible during the Cold War itself -- liberated Kuwait in the brief Gulf War of early 1991, which President George H.W. Bush described as evidence of a "new world order." Historians still debate how much credit for the Cold War's end belongs to Reagan's pressure, Gorbachev's reforms, or the Soviet system's own internal weaknesses -- most now conclude all three mattered together.
Mastery looks like: They can explain glasnost and perestroika's unintended effect, sequence the major events of 1989-1991, and present a balanced, multi-cause explanation for the Cold War's end.
Common stumbles: Crediting a single cause -- only Reagan, or only Gorbachev, or only Soviet weakness -- for the Cold War's end, rather than recognizing historians generally credit some combination of all three.