I can see how much you have thought about this!
I don't know enough about Germany, but in the US most monopolies exist because of the way corporations lobby the government for rules and regulations that work in their favor and basically create a moat around them that makes competition almost impossible.
I think the most damaging monopoly is of money itself. Only central banks can print money, and the use of each nation's currency is enforced by violence (or the threat of violence). I can imagine that without that, different forms of currency or trade could emerge naturally.
