Security "experts" with access to large-scale media organs have expressed concern for at least a decade over the growth of China's navy, and its increasing ability to intervene in situations that we don't want them to--Taiwan, the Spratly Islands, and a few territorial disputes with Japan and South Korea. Non-experts that I've spoken to sometimes think that the US is vulnerable to being invaded by China. With boats. Seriously?
While everyone likes to pretend they're an expert on these things at cocktail parties so they can pick up some cute music major, misinforming other freedom-loving Americans with false vague impressions of the Pacific is the kind of thing that could get the United States into a cold war mentality--and perhaps create a self-fulfilling prophecy--with China.
The US public needs to relax a bit on the China issue. I shall explain why:
1) China's military is not that awesome. It might not even currently be able to conquer Taiwan on its own, and certainly wouldn't be able to if the local US Carrier Fleet (stationed in Yokohama) intervened. It has zero aircraft carriers, compared to the 12 that the US sports.
2) The Japanese, Russians, and Indians have navies, too. Remember them? Right, them. None of them are exactly China's biggest fans, particularly the Japanese. While they may get along, none of them is going to lay back and let one of them run around the Pacific building an unchecked empire. China's navy is divided into a north, south, and east fleet specifically because it has to deal with the Russians and South Koreans in the north, the Taiwanese and Japanese in the east, and the Indians (and Vietnamese, Philippinos, Indonesians, Malaysians; small on their own, but together, enough to be a harassment) in the south.
India currently has an aircraft carrier of its own, is building another one for late this year, and expects shipment of a third from Russia this year, as well. That's 3 aircraft carriers, which is exactly 3 more than anyone in the Pacific has, besides the US. They will not be a force to be trifled with.
The Russian fleet is rebuilding extremely quickly under Putin (and, soon, his puppet), and the Pacific fleet has a number of top-of-the-line Soveremenny destroyers and an extensive logistics/supply/repair fleet to keep them moving.
The Japanese have a stock of Destroyers that rivals the Chinese, despite constitutional blocks on their Self Defense spending. If this ban is lifted, they could quickly grow even stronger.
Ultimately, the US doesn't have to worry about the Pacific too much, as long as all four of these great states keep rising at a pretty even pace. India, in particular, has the growth potential to keep China almost completely in check on its own. So the Chinese won't be invading the US any time soon--I can't say much about Taiwan, but I don't share nearly as much concern over the little island as many American security experts.
And frankly, I'm pretty excited about this naval rise in the Pacific. If the US cannot possibly dominate the region, then the incentive for the US to spend as if it could drops dramatically. We could reduce our carrier fleet number from 12 to maybe 9 or 10, and let the status-quo-loving states of the Pacific keep things peaceful on their own.
Unlike their European counterparts, the powers of the Pacific see no need to free-ride off the military of the US, and they are choosing to depend on themselves for security. And if the primary concern for the US in the Pacific is peace and prosperity (which it should be; Democracy is nice, but it tends to form after prosperity in the Pacific-- see South Korea, Taiwan, Philippines), then self-management on the parts of China, India, Russia, and Japan, is fully in our favor, even if they don't get along that well.
The US should keep a carrier fleet or two ready to move in and make a stand where it has to should it need to, but being the unquestioned superpower in East Asia seems like a dilapidated policy which the US--for the sake of its taxpayers, if nothing more--should drop.