Seems most of you've dodged the queston. It's a hypothetical question....you can't think of what would happen?
1. Europe returns as THE capitol of the world. Probably with England in the leadership position. A slow, inefficent bureucratic system with the European Union will hamper their ability to react fast and decisevly, though.
2. China retakes Taiwan.
3. Japan remilitarises, probably mostly defense forces though. They've become too used to being non-violent to switch back to being Imperialistic.
4. Japan and South Korea become the inventors off all the new research and development products.
5. Canada becomes almost bound at the hip to the UK.
6. South America goes thru a series of small, low tech wars that get rid of drug cartel powers who now have no money.
7. Russia becomes the new working class producer of goods for the world. Not inovative stuff, but lots of cheap products that sell well.
8. The Middle East invades Israel and they respond by nuking the Muslims. Israel ejects all Palestians from their borders. The EU is not yet fast enough to enter the fray to halt any of this. Israel eventually loses and the Muslims do NOT spare any lives and kill indiscriminately. Not all Muslim nations join this union. Those that don't prosper. They might also war ammonst themselves.
9. The EU tightens up and streamlines the inefficiencies of their militaries to each other out of neccessity. Although never as fast to react (too many chiefs, not enough indians), the EU eventually fields as much power if not slightly more than the USA did.
In the end it is a four way toss up between these guys, probably in this order.
1. The European Union (Con)Federation (loose unity = confederation, tight union = federation)
2. Japan
3. Russia
4. China