Don’t forget that the U.S. also has huge space assets, including the GPS system. The Russians had a GPS satellite system as well, but I don’t know if it’s still very operational.
Plus, the EU would be split apart if it came to conflict with the U.S., because there are a number of strong U.S. allies there. And Great Britain would be sure to be on the side of the U.S.
The U.S. also has a tremendous advantage in that it is geographically isolated. The U.S could stage attacks on Europe from any number of places. The Europeans would have to land on the continental U.S. or Canada, and an invasion force would be spotted a long way off and never make it to land fall.
That’s assuming a conventional all-out war, which will never happen when there are huge numbers of nuclear weapons in the world. France has enough nukes to act as a deterrant against the U.S., and the U.S. has enough to wipe out every major city in Europe.
Therefore, there is ZERO threat of a direct conflict between the U.S. and the EU. What is more possible, but still highly unlikely, is that a situation arises akin to the cold war, in which the EU starts militarily opposing U.S. allies or satellites, while also trying to win the hearts and minds of other countries to draw them into their sphere of influence. Such a war would be marked by diplomatic bickering, the occasional inflammation of disputes into short, sharp military interventions, a build-up of militaries on both sides, etc.
But even that is very unlikely. I’d be much more likely to believe that the next threat could wind up being something like the rise of an Asian threat, with China in the middle and perhaps even Russia moving to that side. That would be much more dangerous, because it would expose the U.S. to the combined nuclear arsenals of Russia and China, and potentially a massive conventional army made up of Chinese soldiers with Russian technology.
China is the biggest worry. China is developing a blue-water navy. China wants to be a world superpower, and by most accounts will be one within 20 years or so. China is rapidly developing a very robust space program and wants to land men on the moon. And China’s economy could boom if they continue to restructure along capitalist lines.
If China grows into a superpower with Carriers and a thriving space program, the threat would be to Europe, not the U.S. But the U.S. would come to the aid of its European allies. So it’d be the U.S. and Western Europe against China, some other Asian states, and maybe even Russia if it thought it was in its interests to move that way.