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FOR six decades now, Taiwan has been where the simmering distrust between China and America most risks boiling over. In 1986 Deng Xiaoping called it the “one obstacle in Sino-US relations”. So there was something almost ritualistic about the Chinese government’s protestations this week that it was shocked, shocked and angered by America’s decision to sell Taiwan $6 billion-worth of weaponry. Under the Taiwan Relations Act, passed in 1979, all American administrations must help arm Taiwan so that it can defend itself. And China, which has never renounced what it says is its right to “reunify” Taiwan by force, feels just as bound to protest when arms deals go through. After a squall briefly roils the waters, relations revert to their usual choppy but...