The dilemmas here are best illustrated by looking closely at pre-emptive war. It is a lesser evil because, according to our traditional understanding of war, the only justified resort to war is a response to actual aggression. But those standards are outdated. They were conceived for wars against states and their armies, not for wars against terrorists and suicide bombers. Against this kind of enemy, everyone can see that instead of waiting for terrorists to hit us, it makes sense to get our retaliation in first.

New York Times magazine op-ed piece, May 2, 2004