Randy Barnett, a Georgetown University law professor, discusses libertarian attitudes toward war in this OpinionJournal piece (HT: No Left Turns):

While all libertarians accept the principle of self-defense, and most accept the role of the U.S. government in defending U.S. territory, libertarian first principles of individual rights and the rule of law tell us little about what constitutes appropriate and effective self-defense after an attack. Devising a military defense strategy is a matter of judgment or prudence about which reasonable libertarians may differ greatly.

Barnett notes that “The point of this essay is not to debate the merits of the Iraq war but to inform those who may be unaware that libertarians e down on either side of this issue.”

See also: “Classical Liberalism, Foreign Policy, and Just War”