evidence: China and the Philippines engaged in a tit-for-tat early this week after a Philippine warship sailed near Scarborough Shoal, a barren rock about 120 miles west of the island of Luzon that has become one of the region's hottest points of instability. China claims sovereignty over 80 percent of the South China Sea, pitting it against the territorial claims of Vietnam, Malaysia, Brunei, Indonesia, Taiwan, and the Philippines. The sea's Scarborough Shoal, known in the Philippines as Bajo de Masinloc, has effectively been under Chinese control since 2012 and is at the heart of much of the recent escalation between Beijing and Manila. [...] China moved in on Scarborough Shoal in 2012 after its maritime forces intervened to prevent Philippine law enforcement from arresting Chinese fishermen who were fishing illegally. After a weeks-long standoff both sides agreed to leave the area. The Philippines' forces honored the agreement, but China's did not, and they have maintained a presence there ever since.