Frank Arouet, its far cheaper to trade than invade. The allies in WW2 required nearly 5,000 vessels to cross just over 125 miles of water to reach a part of France that was closely attached to the rest of the country. Take a look at what would be required to invade Australia. In reality you don't need to invade to control. All that is required is to control the trade routes, i.e. S. E. Asia.