The South China Sea is one of the most strategically and economically important waterways in the world. In 2016 more than 21% of global trade was estimated by UN bodies to have transited through it, and it contains extensive oil and gas reserves.
But it is highly contested. China, the Philippines, Vietnam, Malaysia, Brunei and Taiwan all have claims over areas within the 3.5m sq km area, many of which overlap. Brunei is the only party that does not lay claim over any disputed islands, but it does say part of the sea falls within its exclusive economic zone.
The US isn’t a claimant, but says the water is crucial to its national interest and often conducts freedom of navigation operations (Fonops) through the area in a message to all parties.
China’s claim is the most extensive, and most controversial. It marks out most of the South China Sea as its sovereign territory with the so-called “nine-dash line”, claiming historic rights. In 2013 the Philippines took this to an international tribunal in The Hague, which ruled against China. Beijing, however, refused to take part in the hearings and rejects the ruling.
Several claimants have occupied islands, reclaimed lands and built military structures to assert their claims. China’s efforts have been the most extensive, and it also maintains a heavy presence in the area with its navy, coast guard, and maritime militia – a paramilitary fishing fleet – which sometimes conduct dangerous or aggressive actions against other parties.
The decades-long tensions often boil over into standoffs and hostilities. Analysts have expressed concern that hostilities between China and the Philippines, in particular, threaten to escalate.