China has turned the “Century of Humiliation” (foreign attacks on China from 1839-1949) into a powerful weapon. The “Century of Humiliation” is one of the few things nearly all Chinese can agree on. It was a period in which China was humiliated by Western powers (especially Russia and Britain) and Japan. Since 1949, any Chinese politician could gain some instant popularity by coming up with some way to deliver a little payback for the “Century of Humiliation”. Given that the corrupt communist government of China is quite unpopular, senior officials know they can do something about that, at least until the next corruption scandal featuring one of their peers, by scoring some points against any of the “Century of Humiliation” heavies. Actually, any Western nation will do, but the U.S. is the best target (despite the fact that the U.S. tended to be a “friend of China” during the “Century of Humiliation”). America is the sole world superpower at the moment, so it has to be portrayed as Enemy Number 1 for China.
Russia is given a pass because it is still in China’s interest for Russia to be seen as an ally, not a long-time oppressor. The most prominent local bad guy is Japan, which humiliated China for over half a century (from the late 19th century to 1945). But all of China’s neighbors are guilty of at least some disrespect during the “Century of Humiliation” and must be punished. At least that’s a widespread attitude in China and always good for a rousing media event on a slow news day.
Thus the “Century of Humiliation” and the popularity needs of senior officials does much to drive foreign policy. Take, for example, the many territorial disputes which China has, over the last decade, turned into seemingly dangerous diplomatic and military flash points. The most obvious one is the claims China has made on dozens of unoccupied reefs, rocks, and small islands in nearby waters. Recently China declared most of the South China Sea to be part of China because of all those claims. Similar claims with South Korea and Japan have caused these two nations to increase military spending and prepare for more serious confrontations with China. South Korea and Japan have been neighbors with China for the longest time and know how this drill works.
The sad fact is that China has had many “Centuries of Humiliation” in the past, and beating on neighbors who had gotten too independent while China was down was always the response of the Chinese once they were back on their feet. The big potential problems are the outsiders (Westerners) who do not truly understand how one must deal with a China that is strong and looking for respect. Misunderstandings could get out of hand. For that reason, Western nations pay close attention to the consul of their local allies (especially Australia, Taiwan, South Korea, and Japan).
But beyond all this ego maintenance China has economic reasons for its claims on much of the West Pacific. China needs the fish out there as well as any oil and gas under the sea floor. So do the neighbors, but China has more people than all its neighbors (except India) combined. India is a special case because the Indians have nukes and no interest in catering to Chinese demands for respect and deference. Moreover, India is too big (militarily) to bully, as is the case with most of the smaller neighbors. So China is careful not to push India, while being more blunt and aggressive with the Philippines, Japan, and South Korea.