The early years of the twenty-first century have been rife with war and threats of war. Jihadist-related deaths have increased from an average of roughly 2,500 innocents per year from 2001 to 2006 to an average of more than 28,000 per year in 2014-2015. ISIS continues its deadly attacks and genocidal missions across Africa, Asia, and Europe. Russia justifies its invasion of Ukraine and annexation of Crimea. The Syrian civil war continues to be a proxy war involving Russia, Iran, Turkey, Saudi Arabia, Qatar, and the United States.

For Americans, the past few years have seen a number of foreign military provocations. Russia buzzed a U. S. Navy ship and performed barrel rolls over a United States Air Force reconnaissance plane in the Baltic Sea. China recently seized a United States underwater drone in the South China Sea.

Although these types of provocations are not acts of war themselves, and although they don’t even lead us close to the brink of war, they do provide the opportunity to reflect upon a very significant question: what are the criteria that must be met in order for the United States to be justified in waging war?

The existence of such criteria is especially significant in light of the fact that both major political parties have factions that tend to have a “crusader” mentality (see my recent article on 10 signs that a “just war” is really a crusade).

In response to this question, I begin by discussing two flawed approaches to war and peace, then proceed to delineate eight criteria that must be met before the United States would be justified in going to war.

Two Flawed Approaches to War

The view that has just been outlined is known as the “just war” view. It draws upon biblical teaching to argue that deadly force is sometimes necessary because we live in a fallen world. However, not all Christians hold the “just war” view.

Pacifism (Be Peaceful by Laying Down Your Sword)

Some Christians are pacifists. Pacifists refuse to use deadly force because they believe it is evil to do so. Some pacifists will approve of the military using deadly force as long as the pacifist himself doesn’t participate, but consistent pacifists refuse to support any type of violence at all. They draw upon passages such as the Sermon on the Mount, in which we are told that we should love our enemies and be peacemakers (Matt 5:9, 38-46).

Although well-intentioned, pacifism is idealistic and does not make sense of a fuller biblical teaching. It overlooks the Bible’s teaching that God instructs the government to bear the sword (Rom 13:3-5), Jesus used violence to cleanse the temple (Jn 2:15-16) and told his disciples to carry swords in case they needed them (Lk 22:36). Pacifists are right to want peace, but are wrong to think that government should not wield the sword in a fallen world.

Crusade (Seek Universal Peace by Means of the Sword)

Other Christians reject “just war” criteria and support wars of crusade. A war of crusade is religious and/or ideological. It is led by a religious (e.g. imam) or ideological (e.g. Lenin) authority who wishes to defeat evil and impose their vision of the “good.” Crusaders see themselves as waging war on behalf of ultimate good by imposing an ideal social order. Instead of showing restraint in war by, for example, distinguishing between combatants and noncombatants, they tend to want to annihilate the old social order by converting, punishing, or destroying the enemy.

Crusaderism’s own idealistic picture does not make sense of biblical teaching. Although there are instances in which the Bible views a crusade mentality approvingly, those instances are ones in which God himself instructed Israel to go to war (e.g. Num 31:1-54) or in which God will lead a final crusade to defeat his enemies and institute a one-world government (Rev 19:11-21).

Criteria for Becoming Engaged in War

Over the millennia, Greek philosophers, Roman lawyers, Christian theologians, and others have developed specific criteria that must be met if a nation-state is to be justified in becoming engaged in a just war. Those criteria are:

  1. Just Cause: a nation must go to war only if it is defending against an unjust aggression. In other words, a nation should not go to war merely to topple another nation’s leader, install a preferred political or economic system, or expand its own power.
  2. Competent Authority: the decision to go to war must be made by the ruler or ruling body that is responsible for maintaining that nation’s order and security.
  3. Comparative Justice: a nation should only go to war if this war leads to greater justice than refraining from war and tolerating the other nation’s injustice.
  4. Right Intention: a nation may go to war only if their intention is to restore the peace. It may not go to war for the purpose of glorifying itself, enlarging its territory, or humiliating its opponent.
  5. Last Resort: a nation must exhaust all realistic non-violent options (e.g. diplomacy, economic sanctions) before going to war.
  6. Probability of Success: a nation must determine that it has a realistic hope of achieving victory.
  7. Proportionality of Projected Results: a nation must determine that the anticipated results of the war are worth more than the anticipated costs.
  8. Right Spirit: a nation must never go to war with anything other than regret. It should never wage war with a lust for power or delight in humiliating the enemy.

Just as there are criteria for becoming engaged in war, so there are also criteria for a nation’s conduct during the war. The nation must not use more force or do more killing than is necessary to achieve its legitimate military goals. It must distinguish between combatants and non-combatants, avoid using evil means such as rape or the desecration of holy places, treat POWs with humane decency, and cease fighting once it becomes clear there is no chance of winning.


Augustine, the fifth century church father, once wrote,

“Does it displease good men…to provoke with voluntary war neighboring kingdoms (though most wicked) who are peaceable and do no wrong (to neighboring kingdoms), as a way to enlarge one’s own kingdom? If good men feel this way, they are right and I praise them.” (City of God 4.14)

Pacifists, Crusaders, and Just War proponents agree that the world clashes with conflict, and also, that God’s full shalom will not be restored until Jesus returns. Inevitably in our broken world, nations and kingdoms will “provoke…neighboring kingdoms…as a way to enlarge [their] own kingdom.” Thus, not only should Christians themselves seek peace with neighbors, domestic and foreign, they must encourage nations’ leaders to seek peace and to exercise force only after having met specific criteria that ensure the ensuing conflict is justified.


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