The more we lump terrorist groups together and draw the battle lines as a simple binary struggle between moderates and extremists, or good and evil, the more we play into the hands of those seeking to unify groups with little in common. Terrorist groups need to be tackled at root, interdicting flows of weapons and finance, exposing the shallowness of their claims, channelling their followers into democratic politics.

The "war on terror" also implied that the correct response was primarily military. But as General Petraeus said to me and others in Iraq, the coalition there could not kill its way out of the problems of insurgency and civil strife.

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