This is a tough one, because there was alot of stuff going on at that time. When WWI kicked off Europe was doing quite well from the economical standpoint. However, there were massive political tensions which led to WWI. After the war many economies were devestated and Europe had lost all taste for war. All the while, the U.S. intially was becoming an economic powerhouse until the Great Depression. Then comes WWII, which brings the U.S. out of the Great Depression and turns it into an economic superpower. Meanwhile, Europe had to rebuild yet again. During this process the leaders of those nations were losing colonies, which had been supplying them with the raw resources to fuel a big economy. In the end they just could not support the same kind of military and political ambitions as before. Europe's sun had set and the U.S's was rising, and later Japan's sun was rising again as well. However, currently the E.U. (European Union) is an excellent economic machine and is allowing the nations of Europe to flex more geopolitical muscle, while the U.S. seems to be waning. Hope this answers your question.