If only the British had surveyed the whole lot properly and the Chinese had signed up to the maps pre-1914 we wouldn't be in this mess
Actually the Admiralty's Hydrographic Department did survey the whole area remarkably well.
As for China "signing up" to their ownership of the Spratley's and Paracels, they'd been Chinese for hundreds of years and neither the British nor American empires demurred until extremely recently. The Japanese did, but that was only for a few years.
The Vietnamese started to get a bit cocky once they'd trounced the greatest Empire the world has ever known during The American War and now they feel that they've gone a bit far in pinching Chinese-owned mineral wealth from the 9 or 11 dash area. They've instructed Odfjell Drilling to plug and abandon the well they are drilling in China's patch and to withdraw the drillship Metro 1 from the area.
American imperial power in the region is on the wane. They lost major bases such as Da Nang and Cam Ranh and Clark and Subic. They still have the bases which they pinched from Japan in 1945, but in general they are on the wane and everyone in the region knows it.