Many conservatives questioned the wisdom and efficacy of using the U.S. military for humanitarian missions in Somalia in 1993 and Haiti in 1994. More recently, however, voices on both the left and the right have called for U.S. military intervention in Darfur, Congo, and elsewhere.

What should trigger U.S. military intervention? Some observers advocate an expansive definition of the national interest to include consideration of America’s moral obligations. Those who favor a more constrained view of American interests worry that so-called moral missions carry high and frequently overlooked costs, and could therefore distract us from the business of defending America. Should policymakers focus their attention solely on U.S. security, or is the United States obligated to prevent genocide, ethnic cleansing, or wholesale violations of human rights?