You might not notice Second Thomas Shoal from the air. The disputed atoll near the Philippines is a bit larger than Manhattan and sinks beneath the South China Sea’s surface at high tide.

       But diplomats and military officials pay close attention to clashes near the shoal between Philippine and Chinese vessels. The fear is that an incident could turn deadly and prompt the Philippines to activate its mutual defense treaty with the United States.

       That could lead to a nightmare: a war between the United States and China.

       In one previous dramatic episode, Chinese Coast Guard vessels confronted Philippine Navy ones near the shoal in June, footage released by the Philippine military showed. Some Chinese sailors carried knives, and one Philippine sailor was injured.

       Video

       Advertisement

       LIVE

       00:00

       0:21

       0:21

       CreditCredit...Armed Forces of the Philippines via Facebook

       Here’s what’s happening in the South China Sea, and why it matters:

       The sea is valuable and contested. The South China Sea has some of the world’s most productive fisheries, as well as shipping channels that carry about a third of global ocean trade. Surveys suggest that it may also contain large oil and natural gas deposits.

       Advertisement

       SKIP ADVERTISEMENT

       The sea’s features were mostly beyond “the administration and often the awareness” of governments until the late 19th century, the scholar Gregory B. Poling wrote in a recent book. But in the mid-20th century, Beijing laid claim to most of the sea with a sweeping, U-shaped boundary.

       TAIWAN

       CHINA

       Extent of China’s

       territorial claim

       PHILIPPINES

       South China Sea

       VIETNAM

       Exclusive

       economic zones

       of other countries

       BRUNEI

       MALAYSIA

       INDONESIA

       INDONESIA

       MALAYSIA

       250 miles

       CHINA

       TAIWAN

       Extent of China’s

       territorial claim

       PHILIPPINES

       South China Sea

       VIETNAM

       Exclusive

       economic zones

       of other countries

       BRUNEI

       INDONESIA

       MALAYSIA

       250 miles

       Source: Permanent Mission of the People’s Republic of China to the United Nations, Esri, Flanders Marine Institute

       By Agnes Chang

       Subscribe to The Times to read as many articles as you like.