The ethical theory that Christians may legitimately fight in wars, but only when certain conditions are met. Those conditions include the following: the cause must be just; the war must be waged by a legitimate government; the means used must be moral; the war must be a last resort; and there must be a reasonable chance of achieving the goals of the war. The just war theory has been the dominant view about participation in war among Catholic, Lutheran and Reformed theologians. It has traditionally been rejected by Mennonites, Quakers and members of other peace churches. Today it is increasingly questioned in the traditions that have nurtured it, especially with respect to the possibility of a nuclear conflict. See also pacifism.
Evans, C. S. (2002). Pocket Dictionary of Apologetics & Philosophy of Religion (pp. 63–64). Downers Grove, IL: InterVarsity Press.