I think the next century is going to be more about economic warfare than actual physical stuff.
China can cripple the USA almost overnight through trade changes. Look at what happened last week when all China said was that it would diversify its investments a little and not rely wholy on US currency. The dollar hit a real low almost instantly. Now imagine what would happen if China flexed the trade-deficit muscle? We've set ourselves up so that we need them more than they need us at the moment, it's an untenable position that can strike at any time.
China's strong central government (and its willingness to flex that muscle) gives it the power to wield its economy like a whip, and we're blind to it as a nation.
Look at their current industrialization effort. We're bootstrapping their conversion from agrarian to modern industry with every purchase of a 'Made in China' tagged chachke. Look at what happened with Japan in the 70s and 80s, we helped them the same way and almost got thrown off the horse. That was peanuts compared to what a country with the natural resources of China is capable of.
Talk about bombing 3 Gorges and nukes and stuff all you want, but the real weapons over the next century are going to have Visa/Mastercard logos on them.
