Since the end of the Cold War, there has been increasing interest in the global dimensions of a host of public policy issues—issues involving war and peace, terrorism, international law, regulation of commerce, environmental protection, and disparities of wealth, income, and access to medical care. Especially pressing is the question of whether it is possible to formulate principles of justice that are valid not merely within a single society but across national borders.

The idea that justice applies between nation-states may be traced back to Aristotle (384-322 b.c.), who criticized the rulers of Sparta and other regimes for trying to gain despotic power over their neighbors. “[T]o a reflecting mind,” Aristotle said, “it must appear very strange that a statesman should be always considering how he can rule and tyrannize over others, whether they are willing or not.” Aristotle argued that such people are fundamentally inconsistent: “[T]hey are not ashamed of practicing towards others what they deny is just or advantageous in their own case; they seek just rule for themselves, but where other persons are concerned they care nothing about just things.” Aristotle's insight that even the practice of war must be subject to principles of justice helped to inspire the theory of “just war” that was developed during the Middle Ages. In the early sixteenth century, two Aristotelian philosophers in Spain, Francisco de Vitoria and Bartolomé de Las Casas, wrote scathing critiques of the widespread violations of the human rights of native American Indians by the Spanish conquistadors.