A major question of political theory and statecraft is: What justifies the use of force, and when shall it be exercised? This issue is particularly relevant today given recent events in the Middle East. As a nation, we are struggling with many tough issues. Should we attack Syria? Should we launch a preemptive strike against Iran? Should we back a repressive regime in Egypt?

Everyone accepts, as a normative matter, the basic libertarian credo that, to exit the state of nature, individuals should agree to the mutual renunciation of force, without which social order is not possible. This social contract ends bloodshed and angst, allowing human cooperation to flourish. But the implementation of the policy is treacherous. How does society create a state strong enough to control private aggression, but not so strong that it itself becomes a greater source of aggression?

Of course, libertarian theory says that a nation that is attacked can defend itself. But beyond that noncontroversial principle, libertarian theory has nothing to say about a range of complex questions, such as what level of precaution is needed prior to attack, whether a preemptive strike is permissible in light of the seriousness of the threat, the likely success of the response, and the danger of collateral damages. Libertarian theory is also weak in dealing with uncertainty. But this is not simply a deficit of libertarian thinking. No theory can answer these questions. At most, theory informs the debate.

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