The US has been shift more of its attention for the last decade or so, very minimally at first due to the conflicts in the Middle East, and the American public at large is just starting to become aware of this fact.. Given the developments of the last two decades such the recent economic development, excluding Japan, of East Asia, The increasing trade tonnage traveling the pacific and the growth of China as a military power, the US has been focusing more of it's diplomatic, economic and military power in the region.
Firstly, there is the US military presence in the region and the development of new technologies, such as functional laser weaponry, that I wrote about back in April. I mused that the announcement of testing of a functional laser weapons system was more a message to potential rivals in the pacific, i.e China. Now there has been an other announcement, here is an Al-Jazerra link if you can't read Stratfor, that the US military conducted their first launch of the X-47B, a large sized drone that is capable of carrying conventional weaponry. Though the US only has two in development, it signals another major development, a weapons system that significantly minimizes the risk of the lives of US servicemen.
The other point to consider is, that while the X-47B only has a range of 2,100 nautical miles versus the Chinese ballistic missile DF-21 type of 2,700 nautical miles, there is a very real likelihood of range increases in the near future. There is also the possible assumption that the state max range of the X-47B is the recoverable max and not a one way maximum. If that is the case, and in the event that the US finally mass produces those weapons systems, the US could potentially strike at targets without ever risking their military carriers.
Next we have the movements by the US in the region economically and diplomatically. Here is a video from stratfor about recent developments on the Tans-Pacific Partnership, link to the transcript here.
It is very telling that China has not been included in Trans-Pacific Partnership talks. Economic trade and development is surely a reason for the partnerships. But make no mistake, even trade is used as a weapon in the game of geopolitics. The United States is trying to isolate China both militarily and economically to minimize their power in the region. In some respects China has assisted the United States, China's increasing belligerence in the South China Sea over the last few years has pushed nations like the Philippines and Indonesia to increasing military cooperation with the United States.
This is how geopolitics works. When a nation is too powerful to be cowed directly, a group of nations will form alliances and organizations in order to curb their power. Ancient Rome, Imperial Great Britain, and Modern America are rather adept at this. Whether or not China is contained depends on a variety of factors, but at the moment I would say that the ball is in America's court.