Why has the South China Sea become so contentious?

News Snapshot:

The law of the sea is clear and simple enough: a country's territorial sea extends to 12 nautical miles from shore and a country's exclusive economic zone - where the state has exclusive rights over natural resources - extends 200 miles. The problem is that there are a lot of countries bordering the South China Sea - and their claims conflict. That's before you add in China's own extremely expansive claim - the nine-dash line which claims nearly the whole sea as theirs. That was rejected by an international tribunal, a decision which China rejected. That's why features in the...