Frankfurt am Main is the major financial and business centre of Germany with just about all the German banks, as well as the European Central Bank (successor in essence to the Deutsche Bundesbank), and the surrounding region also contains most of Germany's industrial base. Not sure if this was the case pre-WWII or not. As mentioned by others, Munich is also important and so is Dusseldorf in the north but nothing beats Frankfurt. Financially it is very similar to why London is a hub for the U.K.