Taiwan: a sovereignty issue

China strongly deplores and firmly opposes the U.S. State Department's comments on the election results in China's Taiwan Province. China's Ministry of Foreign Affairs released a statement Sunday afternoon, calling the U.S. out for sending a gravely wrong signal to the "Taiwan independence" separatist forces. The response came after the U.S. had congratulated the winners of Taiwan's election and expressed the wish to further the so-called "longstanding unofficial relationship" with the island. Meanwhile, the White House again reiterated it does not support "Taiwan independence". What kind of game is the U.S. playing? Why is China reacting so strongly toward the State Department's message?