Why a dilapidated wreck has become a flashpoint for conflict between China and the Philippines

News Snapshot:

For decades the Philippines have stationed a small contingent of marines on a rusting World War II warship that was deliberately run aground on a submerged reef in the South China Sea. The BRP Sierra Madre, while no longer seaworthy, remains in commission and so technically an extension of Philippines sovereign territory. On the weekend, China's coast guard fired water cannon at Philippine vessels trying to deliver supplies to the troops, prompting an outraged response from Manila. So how did a rusting hulk end up at the centre of this new diplomatic spat and where could things go from here?...