
It's interesting to peruse several maps of the sea, the surrounding countries, and the competing claims. The Economist documents "a mesh of overlapping territorial claims 'which' are mounting."
"Besides a wealth of marine life, the sea is believed to be rich in oil and gas: the “next Persian Gulf” in the words of one excited observer. The countries laying claim to this bounty have all been building up their navies, notably China which this week officially confirmed long-known plans to deploy its first aircraft-carrier. To counter such advances, Vietnam has ordered six Kilo-class submarines from Russia...."

Map and Wikipedia article of South China Sea.