To me, Gorbachev's reforms destroyed the Soviet system and led to the collapse of the communist regime. This happened because the Soviet regime relied on tight control of all aspects of society. Gorbachev's reforms broke this grip and the Communist Party could not find a way to keep power without that control.
Gorbachev's reforms brought more openness and freedom into the political and economic life of what was then the Soviet Union. When this happened, the dam had been broken. When the people were given a little bit of freedom, they wanted more and the old system could not adjust to that. That is why the Soviet Union broke up.
The reforms and the mentality that Gorbachev brought into power from 1985 helped to lead to the Soviet Union's breakup because it was a massive departure from the previous forty plus years of political leadership. Gorbachev sought a new paradigm in his policies and understood that a moment had been reached in Russian history that had to be understood. The previous instability in Russian government, three Premiers in three years, helped set the stage. The Communist party could not afford another "old timer" dying in office, so in choosing Gorbachev, they selected "youth," and as had been seen so often in history, with youth comes a level of change. In the introduction of a Glasnost paradigm that embraced openness in dialogue and self reflection and critique from a governmental standpoint, the totalizing force of the Soviet Communist party was significantly undermined. Perestroika based economic reforms were done in the hopes of tinkering with the Soviet economy in order maximize success. What ended up happening was that these reforms displayed the complete sense of economic ineptitude facing Russia after years of neglect and "spin" from the Communist party. Gorbachev's economic reforms were simply not nearly enough for the massive and seismic problems of the Russian economy, proving that the problem was bigger than anyone had foreseen. As a consequence and coupled with Glasnost, people began speaking out, which as again proven by history, when done with pocketbooks, change is imminent. Finally, the break away of the former Soviet Baltic republics helped to hasten the eventual bringing down of the Iron Curtain.
The break up of the totalitarian U.S.S.R. into 15 democratic states is one of the most important events in modern history. By the time Mikhail Gorbachev was appointed Secretary of the Communist Party of the Soviet Union in 1985 the U.S.S.R. was already on the verge of breaking up: the economy was in a very bad shape and three senior party leaders had died in three years creating a political vacuum. His three important reforms were, glasnost, perestroika and democratisation.
Glasnost or 'openness' led to the rewriting of Soviet history and the previously great leaders were unmasked for whom they really were.
Perestroika or 'restructuring' refers to Gorbachev's failed attempts to revive the ailing Soviet economy. When he took over, the economy was in serious trouble with shortages of even the most basic items like bread but Gorbachev did not want to radically change the way the Soviet economy worked. His half hearted attempts at economic reform were a failure and he became very unpopular.
His process of Democratization resulted in power being shifted from the Politburo to the people themselves. In March 1989, the first elections since 1917 were held in Russia.
All these reforms resulted in the complete dissolution of the U.S.S.R.