Much has changed since the attacks of Sept. 11, 2001, but few American institutions have changed as much as the military.
At the most basic level, it has shifted from a peacetime military to a continuously wartime military, and it has done so for the first time since the United States got rid of the draft.
Just as dramatic is the type of wars that this professional, all-volunteer military—especially the Army—has been fighting. They're not the tank-on-tank battles that soldiers had been training for on the high plains of Europe. They're counterinsurgency campaigns, waged in towns and villages, in which junior officers must assume as much initiative as commanders, and in which all soldiers, even enlisted personnel, must be as attentive to community relations as to combat.