It has been clear to me for some time now that two different ideas are often confused or conflated — preemptive war and preventive war.

What's the difference?

Preemptive war is a strike to gain the advantage when an enemy strike is believed to be imminent. The classic example in recent history is the 1967 Arab-Israeli War. Israel was aware that Egypt and Syria where about to invade. Instead of waiting, Israel struck first and successfully destroyed Egyptian air power before they were able to get their planes in the air. This preemptive strike was justified by Israel because war with the Arabs was virtually an inevitability, and they wished to gain the upper hand.

Preventive war is something else altogether. It is war designed to prevent imagined future war. It is based on a set of suppositions, hypotheses which could prove true or false. At its heart is the idea — our enemies our strong now, but they will be even stronger in the future. Better to attack them sooner rather than later. Better to defeat them before they get any stronger.

This is the same argument used by Curtis LeMay during the Cuban Missile Crisis of 1962, to justify the use of force (rather than diplomacy) against Cuba and the Soviet Union. Fortunately, cooler heads prevailed. Nuclear war was averted. And in fact we avoided war with the Soviet Union from 1949 (when it first tested nuclear weapons) to its collapse in the 1990's, a period of over 40 years.

Arthur Schlesinger has recently written eloquently about the difference. Several passages stand out. Here's the first one. "Looking back over the Cold War, we can be everlastingly grateful that the loonies on both sides were powerless. By 2003, however, they ran the Pentagon."

And here's another. "The distinction between preemptive and preventive war is worth preserving. It's the distinction between legality and illegality."

I would submit it's worse than that, that preventive war is an oxymoron. On its own terms, it just makes no sense.

War does not prevent war. It creates more war. This is not, however, a thinly disguised argument for pacifism. Only that preventive war never achieves the objective it sets out to achieve.

The classic example is World War I, the war that Woodrow Wilson sold to the American people as the "war to end all wars." Needless to say, it did not end war. On the contrary, it ushered in a century of the worst carnage in human history.

Are we really about to repeat this in the 21st?

The loonies like LeMay were pushed back in 1962. Today, as Arthur Schlesinger has ruefully pointed out, they're in the driver's seat.