Coal. Lots and lots of coal. The Chinese are at peak coal, which means they are looking for new avenues to help fill the coal bunkers which are going dry. They are eyeing at expanding their sphere of influence into the South China Sea and beyond. Their military could easily take over the continent of Australia and then begin shipping boat loads of coal back to the mainland. Why do you think they are expanding their rail system like they are? It ain't for moving people fast, it's for moving coal to regions which are running out. Keep the natives happy and that is one front you will not have to fight. Plus if you can blame the Aussies for the coal shortage and not wanting to sell it, why not invade that country and take it plus put the blame on them.