Twenty-first century war adds new risks: more and more often there are no front lines, no central command, no rules of engagement - only a chaotic collision of politics, power, faith and bloodlust. Victims are as likely to be civilians as soldiers.

Having found the bomb we have used it. We have used it against those who attacked us without warning at Pearl Harbor, against those who have starved and beaten and executed American prisoners of war, against those who have abandoned all pretense of obeying international laws of warfare. We have used it in order to shorten the agony of war, in order to save the lives of thousands and thousands of young Americans.

In a guerrilla war, the line between legitimate and illegitimate killing is blurred. The policies of free-fire zones, in which a soldier is permitted to shoot at any human target, armed or unarmed, further confuse the fighting man's moral senses.

What one Predator drone pilot described of his experience fighting in the Iraq war while never leaving Nevada: 'You're going to war for 12 hours, shooting weapons at targets, directing kills on enemy combatants. Then you get in the car and you drive home, and within 20 minutes you're sitting at the dinner table talking to your kids about their homework.'

Like a baseball game, wars are not over till they are over. Wars don't run on a clock like football. No previous generation was so hopelessly unrealistic that this had to be explained to them.

If in some smothering dreams you too could pace Behind the wagon that we flung him in, And watch the white eyes writhing in his face, His hanging face, like a devil's sick of sin; If you could hear, at every jolt, the blood Come gargling from the froth-corrupted lungs, Obscene as cancer, bitter as the cud Of vile, incurable sores on innocent tongues,-- My friend, you would not tell with such high zest To children ardent for some desperate glory, The old Lie: Dulce et decorum est pro patria mori.