evidence: Less than a mile long, Thitu is one of the largest of the Spratly Islands in the South China Sea, some of which are no more than a sliver of exposed reef. But their diminutive size belies their strategic importance: the islands sit in the middle of rich fishing grounds and next to critical maritime trade routes. In addition to the Philippines, Vietnam, Taiwan and Malaysia are a few other claimants of the islands and the territorial waters around them. However, China is by far the main territorial competitor and claims nearly all the waters in the South China Sea, despite a 2016 international tribunal ruling in the Hague that rejected nearly all of its claims. [...] China is also doubling down on its presence in the Spratlys. It has spent much of the last decade fortifying its toehold in the region. Del Mundo, the mayor, says China is also building three more artificial sand bars near Thitu.