What happened to the Soviet Union happened mainly for domestic reasons. It was a failure of the model based on a command economy and dictatorship. The rejection of freedom and democracy, the decisionmaking monopoly of one party, and the monopoly of one ideology all had a chilling effect on the country. That model turned out to be incapable of making structural changes. It did not open up ways for initiative and was overly centralized.
Mikhail GorbachevWe must speak more clearly about sexuality, contraception, about abortion, about values that control population, because the ecological crisis, in short, is the population crisis. Cut the population by 90% and there aren't enough people left to do a great deal of ecological damage.
Mikhail Gorbachev