The division of Germany and Berlin into 4 zones of occupation.
There were a number of decisions taken by the allies at Potsdam concerning Germany. These included how to denazify the country, the prosecution of war criminals and the return of seized territories.
However the most important was splitting Germany into 4 zones of occupation, French, American, British and Soviet. The same happened to Berlin.
As the Cold War intensified this zoning became permanent. The three western zones became West Germany and West Berlin and the Soviet zones became East Germany and East Berlin.
This would last until the collapse of communism and the Berlin Wall in 1989.
