Eric Raymond has a good piece which makes an obvious point that I have I have touched on before: specifically that Europe's demographics suck, and America's don't. Europe's inability to cope with this is made much worse by its large welfare state, with will act ultimately like an unfunded pension scheme.

A couple of other observations.

Japan is even worse than Europe in terms of population decline, although they don't have the welfare state that Europe does. That said, they are really screwed. They will not have ethnic riots because they are ethnically pretty homogeneous. That said, I am sure they may well find other outlets almost as unpleasant.

Normally one would expect the countries of Eastern Europe to be dynamic places, given they have only recently gained economic and political freedom. At the moment this looks true. However, their demographics suck too, and this will eventually catch up with them.

By listening to ancestral 70s lefties prophesying doom, China with its one child policy has engineered a future demographic crisis of its own. It isn't really visible at this point, because they are still feeling the momentum of a huge population boom, but in a couple of decades it is really going to hit. They cannot solve this with immigration the way the US (at least partly) has, as they are too big, but they can at least avoid constructing a welfare state.

India has much, much, much better demographics than China for the long term. If they can use all these people in an economically productive capacity, as they are showing signs of doing, the results could be extraordinary.