Eastern Europe had been a source of unrest and resistance to communist rule and Soviet domination more or less since the Red Army occupied those countries and installed communist governments at the end of World War II. Poland, Hungary, and Czechoslovakia in particular resisted, and each in turn had rebellions crushed by Soviet tanks in 1981, 1956 and 1968 respectively.
But by the mid-1980s the situation had changed. Mikhail Gorbachev, a reformer of sorts, had taken over the Soviet Politburo. The Solidarity labor union, led by Lech Walesa, continued to exist and organize and call for reforms in the Polish government. As Gorbachev allowed Glasnost, openness in Soviet society, he also tolerated more dissent in the Eastern European satellites. The USSR was also less able economically to suppress the Warsaw Pact by force, as its military had been partly committed to the war in Afghanistan in the 1980s. Its economy was shaky.
Large protests took place in Poland, Czechoslovakia, Romania, and East Germany. In August of 1989, Hungary announced it would no longer patrol the Iron Curtain border with the West. It was like opening a floodgate as other East Europeans, free to travel to Hungary, did so with a few belongings and fled to Western Europe and freedom. Gorbachev decided the USSR would not intervene and within six months, the Eastern Bloc of communist nations had fallen like dominoes. Only Romania descended into violence.
So on a wonderful night in November of 1989, having sold my Chevy Nova in my junior year of college and flown to Berlin, it came to pass that I was able to share champagne and sledgehammers with ecstatic West Berliners, tearing down the Berlin Wall one chunk at a time and celebrating like there was, for the first time in a long time, one Germany.