This Should Come as No Surprise
...but the Pentagon has identified China's growing military power as a potential threat to U.S. interests in the Far East, and eventually, the CONUS.
In its annual report to Congress, the DOD said China has "the greatest potential of any nation to compete militarily with the U.S.," although its current power-projection capabilities are limited. The report echoed themes found in last year's study, which warned that Beijing's growing military forces can already alter regional military balances.
Of particular concern is China's build-up opposite Taiwan. According to the report, Beijing has deployed more than 700 short-range missiles opposite the island, giving it the ability to saturate the island's key military and port facilities, hampering the ability of U.S. forces to potentially aid Taiwan. Additionally, China's growing air and naval forces could eventually challenge American control of the seas to the east of Taiwan, further complicating our military operations in the region.
Analysts were also "surprised" by China's growing strategic forces, including recently-deployed mobile ICBMs. Those missiles are designed for more distant targets--including population centers in the western U.S. Beijing is also revamping its military doctrine, to take advantage of new technologies in satellite navigation and precision weapons.
To be sure, China's military still has some significant shortfalls. It's SSBN fleet is microscopic, and its amphibious lift capabilities remain limited. That latter deficiency represents an Achilles heel for the Chinese military machine, limiting its ability to mount an invasion of Taiwan. But, with Beijing's economy roaring along, the cost of building more landing craft and roll-on/roll-off (RoRo) ships can be easily (and eventually) overcome.
The report notes that Beijing has not fully explained the motivation for its continuing military build-up. That must be an input from Foggy Bottom. You don't need a Phd in International Relations to understand that China wants to be the regional hegemon in the Far East, and eventually bring Taiwan back into its fold. To do that, you need a powerful military, able to engage adversaries (read: the U.S.) on equal or near-equal terms. China's continuing military build-up is simply a reflection of those aims.