The US stood down Soviet Communism for 50 years after the Second World War. Since the collapse of the USSR in the early 90's the US emerged as "the world's only superpower."
Once can ask the question, "why shouldn't China be allowed to build up its military?" or "why shouldn't Iran be allowed to develop nukes?" On the surface it appears that the US is simply being a big bully and throwing its weight around. However I think the answer is actually a bit more complex than that. The US is worried about changes to the balance of power that will destabilize the world and increase the chances for a war that no one wants.
During the height of the cold war, the US and USSR each spent vast sums of our wealth to try to "outdo" the other and change the balance of power in its own favor. In the end this lead to a pointless stalemate. Eventually both sides realized how foolish this was and they entered into negotiations to reduce the level of weapons of mbutt destruction (and reduce the risk of a terrible war that would have destroyed the whole world).
I think that China is entering the ranks of the "richer" nations of the world, and the world system will have to take steps to accommodate China at the political and economic level. Much progress has already been made in this regard. (For example China's recent entrance into the WTO.)
U.S. is always superior by default 4831According to former State Department Chief of Staff Larry Wilkerson, the "Cheney-Rumsfeld cabal" - not Bush directly - torpedo'd U.S. foreign policy. However, we're still paying for GHW Bush's limp-wristed...
However it is hard to accommodate a country such as China mainly due to the fact that it has a single-party government, and this government refuses to grant basic political and civil liberties to its own people. I read that China censors the Internet. I recent months they have closed down hundreds of Internet cafes (which are often the only way poorer Chinese can come online at all). Long before the Internet China was censoring the printed press and electronic media. China represses religious groups. It will not allow any political party or organization to be formed that is not part of the single "official" Communist party. The Chinese leaders have demonstrated their willingness to unleash violence against their own people at Tiananmen Square.
Yes, China has made lots of progress in becoming a richer nation, but it still has a very long way to go before it could be brought to the table as an "equal partner" with the Western powers. This is mainly due to the political circumstances inside China itself, and not due to any lack of military power. No amount of new tanks, ships, submarines, missiles or anything else can bring to China what it wants and needs. This will only touch off a new, expensive, and fruitless arms race with the United States. (We have done this before and we know how pointless it ultimately is). The Chinese leaders must make a fundamental decision about whether they think the path forward for China is through war or through peace. I hope they will chose wisely.