BAGHDAD, Iraq — What Maj. Gen. Peter Chiarelli says he dreads most after a year in Baghdad at the head of the First Cavalry Division is going home. He will leave by the end of the month, walk out of the headquarters his troops have built near Baghdad International Airport, stride past the sign saying “Complacency kills – don’t become a statistic,” and head for Fort Hood, Tex. The Third Infantry Division, which stormed into the airport almost two years ago at the spearhead of the American invasion, will take over. Some things come full circle. But other things do...