After the demise of World War II, Berlin was split between France, America, Britain, and Russia. In 1949 the Soviet State of the German Democratic Republic was created, although it was anything but a democratic republic. The GDR is often referred to as East Germany.
On this day July 1st, in 1990, East Germany is re-unified with West Germany by entering the economy using the Deutsche Mark. Prior to this the currency used by East Germany was the East Germany Mark. Using the same currency allows for a homogenous method of purchase, as well psychologically it removes the separation endured during the long years behind the Berlin Wall.
This idea of making a uniform currency has been utilized multiple times, most notably by the European Union which now uses the Euro to alleviate issues of international commerce, trade, and visits. In 1990 it was estimate there were 16 million people living in East Germany. As Germany unified, there was worry that Germany would again dominate all of Europe and the world. Fear of another Third Reich was the initial reason for splitting Germany, yet Germany has prevailed and proven to the world that it will never tolerate a regime like the Third Reich.