Opinion: 21 years after 9/11, the war has not ended for anyone

Twenty-one years after the destruction of the World Trade Center towers in Lower Manhattan, one can ask whether the United States has yet learned the principal lesson of that shocking, savage day. It is a lesson well-known to military planners, yet hard for a nation with allies on its borders and oceans at its sides to believe bone deep. In the starting and ending of wars, the letting of blood and the waging of battle, the enemy has a vote. The day that has come to be known as 9/11 began a war only for us; for the enemy, the war had been raging for years.