Control of the South China Sea is one of the most contentious and explosive diplomatic issues in East Asia. For centuries, various regional powers have laid claim to the sea, which is rich in fisheries and serves as a shipping lane for more than half of the world’s oil tanker traffic.

China maintains fierce territorial disputes with Vietnam, Taiwan, Malaysia, Brunei, and the Philippines over the 3.5m sq km stretch of water that is also believed to have significant oil and gas reserves. At the peak of animosity during the 1970s and 1980s, China and Vietnam used force several times, resulting in dozens of deaths and several sunken ships.

Chinese President Xi Jinping has vowed to “resolutely defend” the region. During the past few years, Beijing has dredged sand on coral reefs to transform them into islands that it uses as military bases, fitted with missile launchers, runways, barracks and radar facilities.

The US has grown increasingly alarmed by the military build up. Washington has become involved in the disputes, backing those that oppsoe China and conducting naval patrols.

In 2016, an international tribunal in The Hague overwhelmingly backed the Philippines in its dispute against Chinese control of atolls near its shores. However, Philippine President Rodrigo Duterte has looked to China as an economic partner and has not pursued the issue.