Matt's got a post full of true bigthink on the multipolarity (present and future) of the word, and our position vis-a-vis the emerging powers of China and India. Read it in full. I, on the other hand, am going to zoom in a bit:
In military terms, I think there's also less here than meets the eye. As India and China get richer, their militaries will grow more powerful. But it's not as if the American military is so powerful right now that we can credibly threaten to invade China or India (or the EU, for that matter). American global military supremacy simply doesn't take the form of giving the ability to just muscle anybody around. In practice, only fairly ramshackle nations like Serbia and Iraq can really be subdued by the force of our conventional arms. Nothing about Sino-Indian growth is going to change that....
The only possible change here would be if China or India were to somehow acquire the ability to deploy power in this manner. That would certainly have important results, but it's hard to see it happening. The gap right now between Chinese and Indian military capacities is huge and, in fact, growing. China is nowhere near acquiring a large fleet of aircraft carriers, for example, and as far as I can tell no one even thinks they're trying to acquire one. What's more, the United States has a global network of military bases and other facilities. China not only has none, but doesn't seem to me to have any ability to acquire one.
Crucially, why would they want one? The end of unipolarity is a bit ironic, as it stems from our efforts to codify America's international dominance. During the Cold War, we engaged in a massive arms build up, both to exhaust the USSR's resources and ensure military superiority. After it ended, we slowed the build up a smidge, but not by much, and George W. Bush was soon elected partially on promises to reactivate the continual improvement of our military.