China thinks it owns the South China Sea. Everybody else disagrees. The dispute is one of the most dangerous flashpoints in Asia--Foreign Policy magazine called it "the future of conflict." China calls the extent of its claim the "nine-dash line."
The U.S. underwater drone recently captured by China was operating in the sea and in 2001 a U.S. spy plane over the sea was forced to land in China and the crew was held for more than a week.
A third of world trade passes through the area and billions of barrels of oil are beneath the seabed. China's claim, within a boundary it calls the "nine-dash line" includes about 80 percent of the sea. An international tribunal has rejected that claim, but its ruling is unenforceable and China ignores it.
China's been building military bases on reefs by dredging up sand. Here's an incredible NYT visualization of that. The U.S., which treats the sea as international waters, regularly sends military ships and planes through the area. China's disputed claims lead to incidents like the drone capture and spy-plane intercept.
Why it matters:
Escalating tensions between the U.S. and China are already on edge after Donald Trump took a call from the president of Taiwan and Rex Tillerson, during his confirmation hearing for secretary of state, seemed to suggest a U.S. naval blockade of Chinese man-made islands in the sea. White House spokesman Sean Spicer took a similar approach saying the U.S. would prevent one country from taking over international territories in the sea.