Through the centuries Christian thinkers have taken different positions on the controversial subject of war. Three broad theories concerning the morality of war for the Christian can be identified: activism, pacifism, and selectivism. Activism asserts that it is virtually always right to participate in war. Strict pacifism insists that it is never morally right to partake in war. Selectivism argues that it is sometimes right to take part in war.
Just war theory is a type of selectivism contending that while war is always tragic and often evil, it is sometimes morally right, just, and practically necessary. Some leading Christian advocates of just war theory have included Augustine of Hippo (354-430), Thomas Aquinas (1225-1274), and Francisco Suarez (1548-1617). Just war theory involves two main moral categories of evaluation.
1. Jus ad bellum (Justness of War)
Concerning the moral justness of waging war, a just war must conform to the following moral considerations:
A Just War will
- Be waged by a legitimate authority (government or state, not private individuals)
- Reflect moral deliberation (last resort after sincere diplomacy)
- Have probability of success (reasonable belief that victory can be achieved)
- Have a just cause (e.g., defense of innocents and freedom against direct aggression)
- Be just in intent (establish peace, freedom, justice; not unlimited destruction of the enemy)
2. Jus in bello (Justice in war)
Concerning the conduct of war, strategy and tactics must be just:
A Just War will be conducted
- With proper proportionality (sufficient, but not excessive force will be used; good should outweigh evil)
- With proper discrimination (noncombatants [civilians or innocents] should not be targeted
Just war theory has been criticized for various reasons through the years (e.g., by failing to appreciate the benefits of a preemptive strike, being unrealistic in its moral expectations, being practically unworkable), yet it nevertheless remains the most commonly accepted position among Christian thinkers when it comes to evaluating the moral considerations of waging war.
For further study on the ethics of war, see John Jefferson Davis, Evangelical Ethics, 3rd ed. (P and R Publishing, 2004) and J. P. Moreland and Norman L. Geisler, The Life and Death Debate (Praeger, 1990).