It’s the slow motion fuse that poses the greatest threat both to freedom of navigation and international law: China’s conversion of reefs and rocks in the South China Sea into airfields and military bases. By claiming its new bases are islands, China not only claims a 12-nautical-mile territorial sea around each one, but also a 200-nautical-mile exclusive economic zone. Multiply that by at least seven, and China suddenly claims the bulk of the South China Sea as its own and not by mere coincidence, oil reserves that potentially rival those of the Persian Gulf.

Under international law, there are three categories for features that break water in an ocean or sea: islands remain above water, even at high tide, and are able to sustain human habitation and economic life; rocks, in contrast, remain above water at high tide but cannot sustain human life; the third category, low-tide elevations, are submerged at high tide. While islands can claim the territorial sea and exclusive economic zone, rocks only receive territorial sea recognition, and low-tide elevations get neither by themselves.