The drill, dubbed SINKEX, was part of the weeks-long Balikatan exercise held annually between the U.S. and the Philippines. This year's edition, the largest yet, saw some 17,000 armed service members participate, including from Australia and France.

U.S. naval drills have become an annual event. But as an expert in international relations, I believe this year's drills mark an inflection point in the regional politics of the South China Sea.

The drills come a year after the Philippines approved a wider U.S. military presence in the archipelago, which China opposed.