"Step down"?
I expect the US to fall down from its position, and probably someone worse like China will take some of the slack, but I don't see industrial capitalism lasting a century and quite likely only a fraction of it, so it will really be the start of a general collapse.
The US, China, the EU, all of them are engaged at an ever-accelerating rate in turning the world's natural resources and the biosphere into consumer products, and waste - an exponentially increasing amount of waste every year.
Everyone will pretend to care about saving the climate, and we'll keep pumping CO2 into the atmosphere, and transform everything.
Certainly, China would not be an improvement, but at least China is capable of rationally planning for the future, and God, the rest of us are sick of America.
It's like living in a trailer park next to a pair of tweakers who have crazed arguments all night and smash shit and periodically one or the other of them runs out screaming, "He's killing me! Help, I'm bleeding!"
Your endless foreign wars, your horrifyingly unlivable cities, your obsession with cars and guns. So juvenile and so aggressive and so very destructive of the planet.
Thirty years amongst you lot was far too long. Things are much better here in Europe.