US seeks to contain China
Since its "return to Asia", the United States is increasingly using the South China Sea as an arena in which to wrestle with China, as indicated by its sending warplanes into the airspace near China's reefs and islands or sailing warships through the 12-nautical-mile waters around the isles in a move to escalate its military deployment in the region.
From the "not-by-name" criticism of China by the G7 at a recent meeting in Japan, to a military deal struck with the Philippines aimed at strengthening their joint naval patrols, the sailing of a Japanese quasi-aircraft carrier to the South China Sea, and encouraging more of its allies to join the game, it seems the US is intent on encircling China.
US Secretary of Defense Ash Carter, in particular, is doing what he can to peddle a "China containment" scheme.