There's a lot of problems with this analysis.
First off, the US doesn't have imperial ambitions. It doesn't annex territory, doesn't maintain colonies. It has few costly international obligations. Even Iraq the US coudl choose to leave any time it wanted.
In addition, the United States only spends around 3% of its GDP on defense. That's trivial by historical standards.
And third, Europe? How does one imagine Europe being dominant in the future? With a declining birth rate, static economies, no, Europe is losing ground as-is.
China will certainly be a major player going forward. But it has a long ways to go still. It has a huge population but much of it is living in a quasi-preindustrial environment. If we're talking 100 years from now then I think you'll find a multipolar world with the United States, China, Japan, Europe, Russa, India, and other countries all being major powers.
And personally, I look forward to that day. The wealthier other countries are, the more likely they are going to want to support the status quo. I still think it a pretty sad commentary on the state of the world when only the United States is able or willing to be the world's police force. In 50 years, perhaps you'll see more multinational cooperation in dealing with threats like Al Quaeda, Saddam's Iraq, Iran, North Korea, etc.