I don't think that anyone can seriously deny the fact that the US's empire is in decline.
The signs of demise are all there. It will crumble.
How they manage this will determine their role for the coming century or so (one country more introvert, one country focussed on the Americas or two or more countries).
Russia is heading towards internal conflict, India won't be in any serious position of power for decades to come and Brasil is a mess.
As for China. Their arrogance, whether they decide to expand territory or if they remain financers, will determine how the world engages with them.
If they decide to expand territory, there is every chance that the world will gang up on them and sort the situation out.
If they retain their current international position (financing to gain influence in various countries) they will probably slip into the vaccuum the US leaves behind.
The latter, at least in the short term, is a more manageable situation. The former could get very ugly, very fast.
China also has an internal conflict which they try to hide from the world, which they try to oppress internally too. And that is the poverty situation for millions of people.
If China can't get a grasp on that, then it will slowly erode them into the same cycle they've always had and within a century a new dynasty... although it's hard to call the current cycle a dynasty... but let's keep matters simple... will knock the current keepers of power off the throne.
The Chinese government knows this. And that's where it is interesting. If they seriously tackle poverty, the middle class will grow and many people will get a better education and that will overthrow (large parts of) the current regime as well.
It will be interesting to see how China deals with this dilemma.
As for Europe. They've positioned themselves as a serious trading block. I reckon that external factors will have little influence on it or its position.
Internal factors could undermine it though.
I reckon it will depend on how well they deal with extremists in their own borders. Poland, Romenia, extreme right-wingism in other States. If they manage to control that or cut the cancer out, they'll do well in the coming century.