Attempts to establish just grounds for war are as old as civilization itself. The seriousness of the attempts, however, and the nature of the difficulties which men encountered in making their formulations have varied from age to age, in accordance with prevailing assumptions and values. The problem of rationalizing war or integrating it into the social-intellectual structure undoubtedly became most acute with the triumph of Christianity, which was committed to peace but lacked the means of abolishing war. Early Christian thinkers were much occupied with the problem of determining under what conditions good Christians might engage in war and, notwithstanding the paucity of the results, there has hardly been any relaxation of the effort in medieval or modern times.