Randy Barnett has further thoughts. I found this interesting:

I realize that some fraction of radical libertarians, whose opinion I respect, believe that there is no such thing as a just war, but most radical libertarians (including most critics of my WSJ op-ed) allow the legitimacy of a defensive war and oppose only wars of aggression. Some antiwar libertarians who oppose the Iraq war as aggression, for example, supported the war in Afghanistan on “self-defense” grounds. And those who didn’t say they would support a war that was truly in self-defense. They simply deny that the war in Iraq fits that description. Yet if they also accept stance (1), as they appear to, then ON THEIR ACCOUNT because a defensive war is waged by an illegitimate government and the rights of innocents were inevitably violated, it too must be opposed.

I’ve never quite understood the arguments of those who claim that they’re not anti-war because they supported the war in Afghanistan, but that they were opposed to removing Saddam Hussein.

Why did they support the war in Afghanistan? Was it, as described above, because it was a “defensive” war? If so, what does that mean? Was it to prevent further attacks? Or was it to avenge 911?

If the latter (and much of the rhetoric seems to indicate that), then it wasn’t a defensive war, except possibly in the limited sense that by making an example of the Taliban we could discourage other regimes from similarly harboring our enemies.

If the former, then it was a preemptive war (that is, we were going to remove a regime, to prevent it from supporting any further attacks). But we’ve been told by this crowd that preemptive wars aren’t acceptable. For instances despite many threats made against Israel (and the Great Satan–us) by Iran, and its continuing development of the means with which to carry them out, we are not allowed to go to war with Iran, because that would be “preemptive” and we’re supposed to wait for them to strike the first blow, as happened with Afghanistan.

Now it turns out in hindsight that the threat from Iraq was exaggerated (though not as much as many war opponents assume), but at the time, we considered it sufficient to need to be preemptive (not to mention all of the ongoing violations of the UN resolutions and truce agreements that Saddam continued to ignore). In that sense, it was a defensive war. So when war opponents claim that we have a right to defensive wars, but practically only allow it to happen after it’s too late to defend ourselves (as occurred with 911), just what do they mean?