A cosmopolitan city on the Eastern edges of the German Republic, Berlin means different things. It was the Capital of the German Empire after unification in 1871 as well as the focus of much conflict during the Cold War. It has not yet reached the same population level as it did at the end of the Second World war. Greater Berlin was nearly 5 million in the closing days of the Second World war. Today it is still less than 4 million.
If you look at the photographs of the city in the years after the War you will see that it is indeed a city of desolation, ashes and ruins. Then it suffered the peculiar fate of being divided between the Four Allied Powers. In the West, French, British and American armies occupied their own zones of influence in what was to become West Berlin. In the East, the USSR had their zone of occupation which was to become the capital of East Germany - the German Democratic Republic. West Berlin was an island surrounded by East Germany and East Berlin
Disputes over access to the enclave in West Berlin led to the closure of the borders in 1948 when Soviet forces blocked transit corridors. The only way to supply West Berlin was by air. This was the Berlin Airlift which was a remarkable effort to supply the 2 million inhabitants of the city by air. To the surprise of all those involved, the airlift worked and in the end the Soviet Union lifted the blockade.
Until 1861, there was a relatively open border between the West and East Germany through East Berlin. Worried by the continual drain on the population as citizens left through West Berlin, the leadership in East Berlin, with Soviet agreement, sealed off the Western part of the city in August 1961. Border controls were introduced and a physical barrier - the "Berlin Wall" was built.
The two German states were to remain in conflict for nearly 30 years after the construction of this wall which divided the city into two. It was often seen as a symbol of division, and the division of Germany into two separate spheres was seen as symbolic of the division of Europe into two separate spheres of influence. On the one hand we had the Federal Republic with its capital in Bonn. The Federal Republic also took on the role of protecting West Berlin, but never formally annexed that city. On the other side we had the GDR "East Germany", sometimes called "The Zone" by those especially hostile to the USSR.
Changes in the USSR and in Eastern Europe in 1989 led to the borders being opened and eventually to unification of the two Germanies as part of the Federal Republic. Berlin became the capital of the newly united Germany.