What justifies American hegemony is not the mere fact that the U.S. has the power to impose itself as a hegemon. What justifies it is the fact that it is by far the most benevolent hegemon in the history of the world.

"Right" and "wrong" have no place in international politics. Nations exist, among themselves, in the state of nature, and in nature there is only power: the ability to do. It is irrelevant whether it is "right" for a nation to impose itself as hegemon. It is inevitable that some national will. The only topic of discussion is: would you like some other hegemon better than the one we have?

We are not the first generation outside of history. You cannot look at say Western Europe and see the decades of peace and cooperation in that region, after centuries of bloody violence, and conclude that it's because modern Europeans are better and more noble people than the ones that lived just a few generations before. No, the world that exists, where France doesn't bulk up its military in response to Germany doing the same, exists because of American hegemony. That is what justifies the exercise of American power.