What's next, after the USA stops trying to rule the world?

I don't like America destabilizing other countries, but America being the global super power has been a net positive, especially because the alternative could have been the British Empire, Nazi Germany, the Soviet Union, or China. I just hope that now America's place is taken by the EU. If it's taken by Russia or China, dassa no good.

the final frontier

Either humanity will be doomed anyways so it doesn't matter, or some other group or nation will pick up the mantle. As much as I'd like us growing out of our infancy like in Star Trek, there are still too many whiny babies in positions of power all around the world that would like a shot at empire building.

They won't, and they cannot. The economic risks is too high. It will have to end in nuclear world-war.