The Soviet Union was at economic breakdown due to the Soviet-Afghan War.
Gorbachev created two political and economic Reforms Perestroika and Glasnost.
Which gave protesters freedom of speech which indeed led to the breakdown of the Berlin wall and the Unification of the Nation.
The Soviet Union released East Germany shortly before its collapse in 1991, and East Germany reunited with West Germany.
The USSR collapsed leaving East Germany free to rejoin West Germany
the berlin wall was torn down