Taiwan has been a bone of contention since 1949 and China is very angry with the arms sale and sees it as a provocation. The U.S. look at Taiwan as an ally and is a guarantor of its sovereignty. This is an intractable situation and is usually handled with diplomatic "kid-gloves", but usually it rears up its head as when China holds military exercises or the U.S.(as in this case)sells arms, that China sees as a threat.
Tibet, which China invaded in the 1950s and claims as part of China, has been an irritant to China ever since, especially because of the Dallai Lama's very visible promotion of its interests. Visiting capitals around the world and making its case. Early on, Obama had refused to meet him, but in a re-ordering of his tarnished image, he has decided to take on the "panda". China however, sees this as an intrusion in its affairs. Bravo to Obama on this one.
Google's suddenly finding its courage, has decided to take on China on the issue of censorship and hacking. China is a totalitarian regime and free speech is anathema. It exercises total control over information(information is power), and therefore will not allow unfettered use/access to the "net" or other source of information..twitter, face-book, you tube etc. China's technological, industrial/commercial, economic development are dependent on access to information, but only for and by the Chinese state, not for private use and/or consumption. China has to maintain a very tight control, in order to ensure that information injurious to it (civil unrest, official corruption, arrests, unemployment, rural protests and so on) are not widely known or disseminated. They are paranoid about this.
China is moving aggressively in the area of new technology .....wind farms, solar energy etc. and tried to "shanghai" and upstage Obama at the recent climate change conference. They are quickly becoming the largest polluter in the world and refuse to join in an international approach (I guess they fear limits on what it can get away with, so no oversight). It can be said however that at the rate they are developing new energy sources, they may soon become an exporter here also.
This brings us to the next area of contention. China ha s a very big trade imbalance with the U.S.A. It is also the banker to the U.S., holding much of America's debt. They have constantly refused to allow their currency to float, fearing(quite correctly) that this will mean the value of the yuan will go up and thus lose their edge against the dollar. China has an unfair advantage (reminiscent of America's in the good old days,when the dollar and America were "kings"), which it refuses to give up. So far no one has been willing to take them on. Obama is signaling that he wants to do so. China is the "huge growing, growling panda, and is baring its fangs and claws. This will be quite a battle and the "little guys" are going to pay a heavy price. We live in a very interesting time.Be on quard.