Berlin has never been a republic.
The Berlin Wall was built by the German Democratic Republic during the Cold War to prevent its population from escaping Soviet-controlled East Berlin to West Berlin, which was controlled by the major Western Allies. It divided the city of Berlin into two physically and ideologically contrasting zones.
East Berlin was the capital city of the German Democratic Republic (East Germany) from 1949 to 1991.
Berlin was 110 miles east of the "Inter German Border," the line that separated East Germany from West Germany.
East Berlin
The Berlin Wall was the important Cold War symbol that was destroyed in Germany in 1989. It was a physical barrier that separated East Berlin from West Berlin and symbolized the division between the democratic and communist worlds during the Cold War. Its demolition marked the reunification of East and West Germany and the end of the Cold War era.
The city of East Berlin only existed from 1946-1989. At all other times it was united with West Berlin as one unified city of Berlin. However, during the aforementioned period, it was the capital of East Germany, also called the German Democratic Republic (in German: Deutsche Demokratische Republik).
Germany & Berlin
During the Cold War the German city of Berlin was split into separate cities. East Germany was a separate city and country. The Berlin Wall was built to divide the city.
The capital of East Germany (GDR) was East Berlin.
Some citizens of East Berlin, during the Cold War era (1945 - 1989) used to want to visit their friends and relatives in West Berlin, or even to move to West Berlin, where the advantages of the more vibrant, free market economy could be had, and the government of the GDR did not want to allow them to do that, for fear that the communist state would become corrupted by decadent western influences.
The Berlin Wall was opened by East Germany (the German Democratic Republic).
East Berlin was controlled by the Soviet Union and aiding them would have been considered an act of war, thus starting World War III