When U.S. Marines were ordered to withdraw from Fallujah last April, I titled my column “Fallujah: High Tide of American Empire.” For the pullback meant that America was either unwilling to take the casualties to crush the Sunni resistance in Fallujah or unwilling to pay the price of Arab rage if they won a bloody battle. Whatever the motive of the generals in ceding Fallujah, it was a retreat. The Islamic world saw it as such. Since then, fighting in the Sunni Triangle, Sadr City, Najaf, and the Shia cities of the south has escalated. When Baghdad fell, Gen. John...