Just War in the Twenty-First Century

Seventeen years ago, religious and political philosophers engaged in a heated debate over just war theory.

The stakes were high in 2003, when the United States, the United Kingdom, Australia, and Poland were contemplating the invasion of Iraq, then ruled by the brutal dictator Saddam Hussein. Those who supported attacking Iraq were vindicated, at least by President George W. Bush’s administration, when it decided in March 2003 to invade Iraq. U.S. forces defeated Saddam’s ragtag military in twenty-one days of major combat operations.

Unfortunately, getting out and staying out of Iraq proved to be a greater challenge. The defeat of Hussein’s army created a security vacuum between warring sectarian Sunni and Shia groups, both of which fought with U.S. armed forces. In his first presidential campaign, Barack Obama called the invasion of Iraq a “dumb war” from which the United States should extricate itself.

Yet just one month after his inauguration, in February 2009, President Obama announced a revision of the originally planned U.S. withdrawal date to enable more time for coalition forces to train the Iraqi security forces. In August 2010, he was finally able to announce: “The American combat mission in Iraq has ended. Operation Iraqi Freedom is over, and the Iraqi people now have lead responsibility for the security of their country.”

Iraqi security forces, however, proved incapable of maintaining peace and defeating various militant groups, especially the Islamic State of Iraq and the Levant, or ISIL. By 2012, ISIL (alternatively called IS and ISIS) was reclaiming former strongholds from which U.S. and Iraqi security forces had previously driven them. By 2014, Iraqi security forces were in disarray, carelessly dropping their weapons and fleeing the battlefield. Islamic State ruled its territory with unparalleled ruthlessness, leading even those who had opposed the original invasion to demand Washington once more intervene. Obama ordered U.S. troops back into Iraq to retrain Iraqi security forces and defeat ISIL. As of March 2020, there were still about five thousand American soldiers in Iraq.

Whatever you think of the original invasion of Iraq (or the return to Iraq to combat ISIL), practically no one expected or wanted U.S. forces to still be engaged in combat operations there, seventeen years after the first U.S. soldier set foot in “the sandbox.”

The Iraq War is a reminder that Americans must carefully consider the reasons—and potential consequences—of war. As American voters contemplate the legitimacy and logic of our continued military deployments, as well as proposals for new ones, a consideration of just war theory, best understood within a Judeo-Christian context, is warranted.

Biblical Warfare

The very first book of the Bible requires the consideration of a just war theory. In Genesis 14 we read that Abram, patriarch of what would become Israel, engaged in battle with a number of kings in the Levant. These neighboring tribes, we are told, had captured his nephew Lot, Lot’s family, and Lot’s goods. The text tells us:

When Abram heard that his kinsman had been taken captive, he led forth his trained men, born in his house, three hundred and eighteen of them, and went in pursuit as far as Dan. And he divided his forces against them by night, he and his servants, and routed them and pursued them to Hobah, north of Damascus. Then he brought back all the goods, and also brought back his kinsman Lot with his goods, and the women and the people (Genesis 14:12–16).

Nothing in this text suggests that Abram (who would eventually be called Abraham) had erred in his military decision. Indeed, the very next story is of Abram celebrating with the neighboring priest-king Melchizedek, who declares that God had “delivered” Abram from his enemies. The implicit message in this account is that Abram was justified in fighting those who had kidnapped his family.

The Old Testament consistently testifies to other Israelites going to war with the explicit approbation of their God. Moses and then Joshua, at God’s command, bring the chosen people into the Promised Land, defeating and expelling idolatrous people groups. Various judges of Israel, Samson most famous among them, wage war against the pagan Philistines. King David conquers Jerusalem and enlarges the Judaic kingdom for the sake of God. The Deuterocanonical books, in turn, praise the military exploits of the Maccabees, who rebel against their idolatrous Greek overlords and reestablish, albeit briefly, a Jewish state.

Some might have speculated that all this endorsement of war would end once Christ’s message of peace and willingness to suffer, and not inflict, violence had been published in the New Testament and preached widely. Instead, we see the opposite.

After his allegedly providential victory at the Milvian Bridge in 312, Constantine legalized and formally promoted Christianity in Italy. Ecclesial leaders in both the Eastern and Western halves of the Roman Empire blessed Christian armies, such as those of the seventh-century Byzantine emperor Heraclius in his wars against the Sassanid Persians and the eight-century Frankish king Charles Martel against the invading Arabs.

And how can we forget the Crusades? Catholic religious authorities sponsored this series of holy wars over several centuries, first as a just response to Muslim conquests of historically Christian lands across the Mediterranean, and later against various other groups, such as Albigensian heretics and pagan Slavs.

How Just War Theory Developed Through the Centuries

Just war theorists in the ancient and medieval periods offered a number of defenses of military actions taken throughout history, ranging from that of Abraham to Louis IX of France.

St. Augustine of Hippo, writing in the fifth century, argued that war is legitimate in the case of obedience to God’s laws or national self-defense. In his City of God, he writes:

They who have waged war in obedience to the divine command, or in conformity with His laws, have represented in their persons the public justice or the wisdom of government, and in this capacity have put to death wicked men; such persons have by no means violated the commandment “Thou shalt not kill.”

Indeed, it was Augustine who originated the phrase “just war,” as one conducted by wise men.

Following the narrative of Scripture, Augustine recognized that God at times commissioned and endorsed war, such as the Israelite invasion of Canaan after the Exodus. Augustine also offered a second form of permissible war: that conducted “in conformity with divine law.”

Unpacking the specific circumstances for such a category would be done by later thinkers. Perhaps foremost among them was St. Thomas Aquinas, who, writing in the thirteenth century, provided three necessary conditions for a just war.

First, a just war is one waged by a properly instituted authority, such as a political state. In other words, illegitimate political authorities, or those without proper justification or capability, should not wage war. For example, a rogue nobleman who wages war without his sovereign’s approval is disqualified. Or we might think of some multinational corporation that possesses its own security forces and, in defense of its economic assets, wages war to protect or expand them.

Second, a just war is conducted for a good and just purpose, not self-gain or as an exercise of power. This might seems straightforward, though what constitutes a “good and just purpose,” as debates over Iraq demonstrated, can be contentious.

Third, those who perpetrate just wars must be motivated by an intention to secure peace as quickly as is reasonably achievable. In other words, states should seek to end bloodshed as soon as possible, rather than maximize damage to one’s enemy.

In 1526, Martin Luther brought the role of the conscience into just war theory. He writes in Whether Soldiers, Too, Can Be Saved: “A second question: ‘Suppose my lord were wrong in going to war.’ I reply: If you know for sure that he is wrong, then you should fear God rather than men, Acts 4 [5:29], and you should neither fight nor serve, for you cannot have a good conscience before God.” In other words, if someone’s conscience deems a war to be unjust, it would be neither right nor safe, to borrow another Lutheran phrase, to violate one’s conscience.

Similarly, in Temporal Authority, Luther writes: “What if a prince is in the wrong? Are his people bound to follow him then too? Answer: No, for it is no one’s duty to do wrong; we must obey God (who desires the right) rather than men [Acts 5:29].”

Some Basic Just War Principles

In the modern era, the conditions for just war have been more clearly and formally articulated, especially by the Catholic Church. The Catechism provides four strict conditions for “legitimate defense by military force.” These are:

• The damage inflicted by the aggressor on the nation or community of nations must be lasting, grave, and certain;
• All other means of putting an end to it must have been shown to be impractical or ineffective;
• There must be serious prospects of success;
• The use of arms must not produce evils and disorders graver than the evil to be eliminated. The power of modern means of destruction weighs very heavily in evaluating this condition.

The Catechism continues: “the evaluation of these conditions for moral legitimacy belongs to the prudential judgment of those who have responsibility for the common good.”

Just war theorists—both Catholic and non-Catholic—have elsewhere referred to and expanded on these principles under the heading jus ad bellum, “the right to go to war.” These principles can be summarized as “just cause,” “competent authority,” “right intention,” “probability of success,” “last resort,” and “proportionality” (i.e., the benefits of war must be estimated to be proportional to the evils it will bring).

Others have added other terms and conditions, such as a presumption against war. Of course, there’s always fierce debate over whether all these criteria are necessary to engage in just war, and when exactly they have been satisfied.

Just War for a Twenty-First-Century World

As we consider conflicts in the third decade of the twenty-first century, I’d argue another condition, perhaps most closely connected to probability of success and proportionality, is also worthy of consideration: the peculiar nature of war and international geopolitical stability in our century.

Military theorists have emphasized the rise of “fourth-generation warfare,” meaning that state actors have increasingly battled nonstate actors in asymmetrical conflicts where the line between combatant and civilian is blurred, and where militaries are frequently engaged in counterinsurgency (COIN) and nation building. The latter is in a sense a reflection of the former: wherever modern nation-states dissolve (e.g., Iraq, Syria, Libya), we witness more ambiguous, bloody, endless conflicts involving innumerable actors.

In an military era defined by easily accessible IEDs; small arms like Kalashnikovs; social media propaganda; populations susceptible to religious or political radicalization; and global networks of ideological brothers-in-arms, we have a recipe for prolonged conflicts like those in Afghanistan, Iraq, Syria, and Libya.

Any consideration of war needs to take such factors into calculation, because foreign powers like the United States and NATO are liable to aggravate rather than resolve stupefyingly complex geopolitical dilemmas. And once we’ve unseated a political power, however inchoately it resembles a functioning nation-state, it will prove stubbornly difficult to forge a new one, as Iraq so clearly demonstrates. Determining the probability of success is probably the most nebulous of the just war criteria.

As our seventeen-year engagement in Iraq suggests, it’s also likely the most important.

About the Author

Casey Chalk is senior writer for Crisis magazine and a contributor at the American Conservative and New Oxford Review.