What About the Other War?

In Afghanistan, a nation of skirmishing warlords and guerrilla fighters who strike quickly and then vanish, it's difficult to tell when one conflict ends and another begins. Last week, the biggest U.S. battle in Afghanistan in 10 months provided the latest reminder that the U.S. is still far from achieving a lasting peace in the strife-torn countryand that the Islamic jihadis arrayed against American troops and the government of Hamid Karzai are preparing to rachet up their terrorist war.

The battle might never have happened if not for a gruesome stroke of luck. On Jan. 27, U.S. troops...