Never before in its history has China's well being been so dependant on sea trade. For thousands of years, China was a "continental power." That is, a nation that produced all it needed, or obtained it from neighbors via a shared  land border. Only luxuries came in by sea. China is now importing nearly six million barrels of oil a day, a figure which is up a third from last year. China's export industries turn out so much stuff that last year, China passed the United States as the world's largest cargo handler.  So China's growing fleet of warships and patrol aircraft should come as no surprise. But other nations in the region (South Korea, Japan, Indonesia, the Philippines), are also very dependant on seaborne trade. Who shall control these sea lanes that are so important to all? Right now it's the United States Navy. China is not comfortable with that.