which is precisely the point. In this world, there is only room for one global blue water navy. If you have two or more, it's certain to create friction and rivalries that would eventually. China is content to let the US play global cop, let the US pay for securing world peace while other countries get the benefit of such peace. That is a cynical view of things but I tend to be a cynic.
If the US needs more money to finance any potential wartime ventures, China buys more US treasury bonds. Like they did during the Iraq war, and in return, US returns its gratitude to China subtletly by allowing Chinese firms to participate in reconstruction projects and arms contracts like buying patrol boats and guns for the newly constituted Iraqi armed forces.
Much of the same argument can be said about Japan. Japan's economy is very dependent on its sealane lifelines. But Japan is content to let the US do its protection and pay its dues such as purchasing more Treasury Bonds. Japan is the leading owner of US bonds and no surprise, China is no. 2, and both lead far away from the rest of the pack.
Worldwide the US did deploy its sailors and marines for over 100 years, but not in the capacity of global cop, which was Britain's role until the end of WWII. Certainly the US conquest of Hawaii, the Philippines, Guam, Cuba and Puerto Rico via the Spanish-American War cannot be considered a global cop action. The US played its role of global cop after WWII and the sunset of the British empire as the only country still standing that could stand up to the Soviet Union. Pre-WWII, US politics are very much conservative and isolationist (it's your problem not ours), the kind that Pat Buchanan now echoes. You only need to look at some people like Joseph Kennedy (the senior Kennedy) which reflects that sort of sentiment, and why the US came quite late in WWII (end of 1941, when German and Japanese aggression began as early as 1937).
The reason why China and Japan cannot play regional cop is because of bad blood. If you have two members of one family fighting one another, you need a mediator or third person, preferably someone distant and out of the family. Naturally someone from the outside has to come in as cop and mediator, and that role has fallen to the US.
It is not in the security of China to fight the US, everyone knows that. And neither is it in the interest and security of the US to fight China. Aside from posturing, everyone knows the US and China is now too interdependent. Both countries are also politically agile and flexible enough to prevent any need to come to blows because there will be no lack of peaceful alternatives.
A large developing blue seas Chinese fleet can easily be miscontrued and that will start an arms race in the region. Soon the Japanese and Korean navies will all buff up, and ten to twenty years from now, it may reach to a point, the global cop may not have big enough muscles both military and financial to stop our future buffed up Chinese, Japanese and Korean fleets from having a go for control of all three China seas, its sealanes and vital natural resources.
Likewise, a withdrawal of US fleets from the Pacific region will also create an arms race. The Japanese will feel that they no longer have the US umbrella protecting them and will start to build up, while the Chinese will think that without the US, which served as a cap on Japanese military ambitions, there will be no cap to the Japanese, and will build up. Caught in between the two are the Koreans, who will likewise react with their own build up. And when each of them will try to protect the so called lifeblood sealanes---which are often one and the same for all these countries, you may be headed for a collision point. Another collision point is that these countries are also disputing oil and fishing rights on certain territories and islands and all three show no signs of compromising. When you get into a situation when the world starts running out of oil reserves (which may get critical in the next 20 years), the friction point on underwater oil reserves will start to rise.