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A more graphic demonstration of the intractable morass in Afghanistan it would have been difficult to imagine. On Tuesday, the Taliban attacked a police checkpoint in the far west of the country, killing three officers. These fighters then moved on to a nearby village where they executed three civilians whom they accused of spying for the government in Kabul. The Afghan security forces called in the US military for support. But in the subsequent air strikes, scores of innocent Afghan civilians, including women and children, were killed.

The US military had every right to go after the murderous Taliban. But this accidental bloodshed will merely increase the alienation of the local population and further undermine the authority of the central Afghan government.

The...