Human history
Communism became less popular when it became clear that it could not promote economic growth as well as Western states and that it was not suited for a reform that allowed freedom of speech for everybody. Therefore, the Soviet Union forced Hungary to give up its reform in 1956, it favored the building of the Berlin Wall in 1961 and it stopped reform in Czechoslovakia in 1968. When in 1988/89 Gorbachev made clear that he would not force the countries of the East block to stick to Communism the Berlin Wall was torn down in 1989 and the Soviet Union collapsed (1991). Then the United States was the only superpower left.