What obligations do nations have to protect citizens of other nations? As responsibility to our fellow human beings and to the stability of civilization over many years has ripened fully into a concept of a "just war," it follows naturally that the time has come to fill in the outlines of the realities and boundaries of what constitutes "just" humanitarian intervention.

Even before the world changed radically on September 11, policymakers, scholars, and activists were engaging in debates on this nettlesome issue--following that date, sovereignty, human rights, and intervention took...