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The People’s Republic of China reacted to Washington’s announcement on Friday that it will sell defensive weapons to Taiwan worth $6.4 billion with customary bluster. The Foreign Ministry protested to Jon Huntsman, the American ambassador, and announced that a range of military and economic programs between the two countries would be placed in abeyance.

China is never happy when weapons are sold to Taiwan, but this time Beijing threatened to boycott American companies, including Boeing and Raytheon, involved in the deal.

Since its 1949 civil war and the Communist takeover of the mainland, China has regarded Taiwan as a breakaway island. ...