Three weeks after the fall of the Berlin Wall, the East German parliament (Volkskammer) voted to strike the clause from the constitution that guaranteed the Socialist Unity Party's monopoly on political power. The vote formally ended over four decades of one-party Communist rule in East Germany and cleared the way for free elections and eventual reunification with West Germany less than a year later.
The speed of East Germany's collapse stunned even the people living through it. On November 9, 1989, the Wall fell amid chaotic, almost accidental circumstances after a bureaucrat misspoke at a press conference. By December 1, barely three weeks later, the parliament that had rubber-stamped Communist rule for over forty years voted to erase its own party's constitutionally guaranteed supremacy.
The Socialist Unity Party, or SED, had controlled every lever of East German life since 1949 through the Stasi secret police and a pervasive surveillance state. Its leader Erich Honecker had been forced out in October as protests swelled, but the constitutional change on December 1 was the formal death certificate for the one-party state, even as party structures technically persisted for a while longer under new leadership.
Within days, the entire SED Politburo and Central Committee resigned en masse. Free elections followed in March 1990, and German reunification was completed by October of that year. The December 1 vote is often overshadowed by the more photogenic image of the Wall falling, but it was this quiet parliamentary act that made the revolution legally irreversible.