US vs China: destroyers and aircraft carriers wait in the wings

A group of US Navy ships arrived to the South China Sea on 3 March. Tactical force comprises John C. Stennis aircraft carrier, two destroyers, two cruisers and the 7th Fleet flagship. China in its turn dispatched destroyers to the Woody island, which is under its control. Why does the US go towards confrontation with China?
Leonid Krutakov, political scientist:
The region which produces over a half of goods for the whole world by itself is naturally of strategic importance for the Americans. They declare it openly in their foreign policy doctrines that no one among outer players should approach the military potential of the US. But it is also noted there that nobody should grade up to the economic potential of the United States. Thus, it's a purposeful policy.