South America, look at Brazil: developing and largely stable democracy, growing population, largely quite young, and large untapped natural reserves.
The US, by contrast, is largely tapped out on the resource front, has an aging population, and overburdened state and a falling birth rate.
China has a powerful economy, but not per capita, a large democratic deficit and a demographic time bomb that will hit when all those young men realise there are no women fro them to marry and procreate with. Like the US it is also largely tapped out on the resource front, which is which is it why imports massive materials.
Russia shares a border with China, had limited natural resources remaining, a large democratic deficit and a growning and decrepit infastructure whose modernisation is hampered by rampant corruption and cronyism.
Europe, seperately or as the EU, has all the problems of the US (including rising religious fundamentalism) and a democratic deficit.
Whatever the shape of the future, it won't be what we are expecting, but if Europe wants to be powerful again then she will have to go to war and take something from someone else. As you said, power is relative - it is also zero sum.
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