The term has the principal meaning of armed conflict between or among nations or groups of people; by extension it also can refer to an intense, protracted struggle not involving arms. In this latter sense Christianity since the early centuries has encouraged the idea of the "soldier of Christ" (miles Christi) and the "army of Christ" (militia Christi) engaged in spiritual combat with evil as an alternative calling to that of military service on behalf of the state. Taking this seriously implies the moral rejection of war as armed conflict among peoples. Yet the majority of Christians over history have accepted such armed conflict as characteristic of life in a yet unredeemed world and have sought to define the limits of their participation in it. A "crusade" or "holy war" theme has recurred occasionally: in such wars God has been represented as calling Christians to take up arms and as fighting along with them. A more continuous tradition has defined the idea of "just war," in which Christians may morally participate according to the guidelines laid down in the tradition; by contrast, Christians must not take part in unjust wars.
In practice, Christian thought on war in any age has focused on the problems posed by war in that historical context. The attitudes of the early church were shaped in part by the character of imperial Roman military service, those of the Middle Ages by chivalric warfare and by the threat of militant Islam. In the context of the 20th century, discussion has focused chiefly on the destructiveness of contemporary warfare and the heavy economic burden imposed by military spending. Most recently these two concerns have been raised more specifically in connection with nuclear weaponry. A secondary contemporary issue has been argued sharply in some quarters: how far "wars of liberation" may be just and how far a Christian can or must participate in them.
See Aggression; Conscription; Crusade; Deterrence; Just War, Militarism; Nuclear Warfare; Pacifism; Peace; Resistance; Revolution.
This article (and those recommended at the conclusion) appears in The Westminster Dictionary of Christian Ethics (1986) which may be ordered at: http://www.amazon.com/exec/obidos/tg/detail/-/0664209408/qid=1044021843/sr=1-1/ref=sr_1_1/002-4440953-2854417?v=glance&s=books
Please see "Killing and Murder" in "The Bible" subsite of www.philosophy-religion.org/. Also, please consult the final chapter on war in Living Issues in Ethics (available in the Textbooks subsite).