...won't be a military war; at least, not on the whole.
Envision this scenario; the world markets are currently overvalued. Severely so; witness Wall St's shaky week so far. When the big crash happens, people in the US are likely to suffer. The US's probable response to this will be to become more protectionist and isolationist in outlook on the world; placing US interests before global interests (at least, even more than usual). If this coincides with a Republican majority in the 2000 elections, the US will become a severely inward-looking state; and will try to use its power in the WTO and similar organisations to improve the US's position at the expense of trading partners.
There is currently one serious rival to the US superpower; a single Europe that is actually integrated reasonably efficiently. The EU has the potential to be a larger economic superpower than the US; to begin with, the US has the greatest trade gap in the world and is actually much more wasteful in consumption than the EU. What is the standard US behaviour with regard to any external threat to their primacy on the world stage in any sphere?
It's just a thought, but the trade wars this year could just be the start of something far larger. And the first group who will have to be won over are the US public.
Watch out for films that portray the EU (or EU nationals as "the bad guy" coming out of the US film industry in the next year; if this scenario is even vaguely accurate, we should see a resurgence in films portraying the all-American way of life as superior to European culture and people. It's just a thought; watch this space; and watch the attitudes of US politicians with regard to the EU...