I'm very sympathetic to the view articulated by Brad DeLong and John Quiggin (here and here) that international law and the United Nations Charter essentially provide a sufficient basis for thinking about when the United States should and should not use force in world affairs.
In particular, the seemingly commonsense objection that this is airy idealism that can't be put into practice because the bad guys of the world can't be trusted to play along turns out to hold very little water. It's true, of course, that the bad guys of the world can't be trusted to play along, but the Charter itself and international law more generally provides amply justification for the use of force to punish bad actors who insist on waging aggressive war. There's no question of seeking a "permission slip" to literally defend the country against attack, the question of permission slips acts, rather, as a constraint against more grandiose forms of meddling.
I do, however, have two worries about this doctrine. One is that some of our thorniest foreign policy issues -- in particular Taiwan -- have a somewhat murky legal status. The other is that saying one should act in accordance with what the UN Security Council is prepared to authorize doesn't actually answer the question of what the United States, as a leading member of said Council, should be trying to get permission to do. In general, though, I'm very much in agreement with Quiggin about this question and especially with the points he makes in his followup.
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