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Afghanistan is a just war, and a just victory requires the reconstruction of the country. So I have argued for more than ten years with friends, family, and colleagues. My belief in its justice led me to fight in it as a soldier with the U.S. Army in 2002, study the region as an intelligence analyst with the Central Intelligence Agency, and advise two presidents on its conduct as director for Afghanistan and Pakistan on the National Security Council staff.

After the attacks of 9/11, few needed convincing. The initial campaign to overthrow the Taliban, who chose to harbor and protect al-Qaeda, was plainly justified self-defense. The Taliban refused to hand over members of al-Qaeda and thereby became active abettors of the terrorists’ aggression. But even then I felt that defending ourselves was not the end of the matter. Justice involves more than overthrowing the Taliban and getting Osama bin Laden.

Even after our success in removing the Taliban and killing Osama bin Laden, the war still can be justified as self-defense: of ourselves, our allies, and the global liberal order. It can also be justified as the requirement of jus post bellum, our duty to establish a lasting peace that we incurred following the initial invasion and overthrow of the Taliban government. Finally, it can be justified as a defense of the oppressed, punishment of the wicked, and restoration of the moral order. This is not a call for an American empire. The United States cannot simply provide order unilaterally—if we could, we would be a world government. Nor am I echoing the realists’ call to sustain American hegemony for its own sake. It is not realpolitik that should drive American policymakers to sustain American hegemony, but moral duty.

The Taliban retain ties to al-Qaeda and have consistently refused, even today, to sever their relationship with or denounce the group. If the Taliban retake power in Afghanistan, they are likely to invite or tacitly permit al-Qaeda or like-minded groups to reestablish a presence in Afghanistan, an outcome that surely will threaten the safety of Americans.

A number of foreign policy experts disagree. Some believe al-Qaeda has been effectively defeated, others that the Taliban are unlikely to allow the group back into Afghanistan. Perhaps, but we must not adopt an overly narrow understanding of self-defense. All acknowledge that the Taliban pose a direct threat to the current government of Afghanistan and that we should share in its entirely just desire to defend itself. Our government has made repeated and explicit promises to the Afghans that we will help them defend their country, most recently by designating Afghanistan a Major Non-NATO Ally as part of the U.S.–Afghanistan Strategic Partnership Agreement of 2012. Even if the war is not a war of self-defense by the United States, it most certainly is for the Afghans defending against Taliban aggression—Afghans to whom we have promised aid and assistance.

A cynic might dismiss our promises and alliances as rhetorical flourishes that count for little when we calculate our national interests. This is short-sighted. Alliances are a means for states to share the burden of self-defense with others who face a common threat. The strongest alliances formalize an existing relationship between states whose security is so intertwined that neither can feel safe without the other. This sometimes requires a state to involve itself in an ally’s conflicts, even if the threat seems distant.

That was true of the United States and Europe in the Second World War. Germany did not attack the United States—Japan did. But American involvement in the European war was plainly just. The Europeans were waging a justified war of self-defense against the Nazis but lacked the means to win. President Roosevelt understood that the Nazi conquest of Europe was a clear threat to the United States and our way of life. American involvement was a matter of helping others to defend themselves and thereby for us to defend ourselves. The United States, Europe, and the embryonic “United Nations” shared interests so closely that the American war against Nazi Germany was a justified war of self-defense: The “self” we were defending included anti-Nazi forces everywhere.

Our current commitments in Afghanistan follow a similar logic. The Afghan government’s entirely justified war of self-defense against the Taliban directly concerns American security, not only because of possible ties between the Taliban and al-Qaeda but also because of the wide array of interests the United States has across South Asia. Pakistan’s stability and the security of its nuclear weapons will hardly benefit from a Taliban takeover or a civil war next door. The transnational drug trade and Iranian regional influence are likely to grow if Western forces withdraw under unfavorable circumstances.

The United States and Afghanistan share common interests because we face common threats. Our commitment of forces in Afghanistan is not only a function of charity to an oppressed people but also reflects the requirement of our government to protect us. The corruption of the Afghan government does not deprive it of its right to defend itself from even worse evils, nor does this rule out our assistance. We allied with the Soviet Union to defeat the Nazis.

This broader way of understanding the right of self-defense—to defend our allies and our common interests with other nations, not just our territory—points to a more expansive way in which the war against the Taliban can be described as a war of self-defense: It is a war of collective self-defense by the international community against a global threat.

Counterinsurgency expert David Kilcullen argues that we should understand violent Islamist movements such as al-Qaeda and its allies as waging a global insurgency against the liberal world order. In this view, whether or not al-Qaeda has been defeated is irrelevant. Bin Laden’s group was only the most famous of a global network of like-minded jihadist terrorist groups that threaten global order. America, as (still) leader of the free world, is justified in helping organize global self-defense against violent Islamist movements anywhere in the world. The Taliban threaten America because they are part of the jihadist attack on the West and the liberal order we uphold.

This does not mean that the United States should have a direct combat role against every Islamist insurgency in the world, something that would involve American forces fighting not only in Iraq and Afghanistan but also in Egypt, Saudi Arabia, Chechnya, Malaysia, Indonesia, Somalia, Turkey, Pakistan, and elsewhere. Kilcullen rightly specifies that our role should be to “disaggregate” the global insurgency. This involves severing the links that tie local, provincial movements to the global jihadist movement, while bolstering local police and security forces with training and equipment.

The tools of a “disaggregation” strategy are diplomacy, law-enforcement coordination, border control, disrupting terrorist finance, foreign aid, and security assistance. But a direct American combat role is justified and necessary where the jihadist insurgency threatens to overwhelm local governments or threatens broader regional instability. Afghanistan and Pakistan—al-Qaeda’s historic headquarters, the location of its senior leadership, supported by the densest network of jihadist groups in the world—is such a place, and perhaps the most significant place.

The idea of global self-defense is admittedly expansive. In classic just war writings, the “self” of self-defense typically justifies sovereign states or an alliance of states defending themselves against conventional threats such as large armies marching across borders, concerns characteristic of the early modern era, during which a great deal of just war doctrine was formulated. But the contemporary security environment has changed. States have grown more interdependent, thanks to technology, globalization, and a deep network of international institutions.

To a great degree, sovereign states have allowed themselves to become interdependent because interdependence serves to underpin the liberal world order created by the Allies after the Second World War: a system of open trade, humanitarian norms, and rules-based institutions from which they benefit and to which most have voluntarily subscribed. This interdependence means that it is easier for a threat against one to translate into a threat against all; some threats are truly global because there is a world order that can be threatened. The terrorist attacks on 9/11 killed twenty-eight South Koreans, forty-one Indians, and forty-seven citizens of the Dominican Republic, among thousands of others.

These realities justify a new application of just war thinking, one that recognizes collective self-defense against global threats. Any threat to the liberal world order—terrorism, piracy, territorial aggression, or proliferation of weapons of mass destruction—is a threat to the states that benefit from that order. Collective action to defend the world order is a form of self-defense. The United States has a special duty in this context. American policymakers have long recognized that because the United States is the leading power, architect, and beneficiary of the liberal world order, America has a unique responsibility to organize global efforts to sustain it.

This is not, as I said, a demand that American policy serve American interests. The liberal world order is just—or, at least, more just than the alternatives—and therefore defending it is a moral duty, whether or not it is in our interest.

Of course, it is in our interest to defend it. We cannot pretend to be a disinterested party. We benefit greatly from the liberal world order. But we should not allow that to become an excuse for inaction or paralysis. A healthy suspicion of our own motives should always lead us to prefer the inconvenient accountability of partners, allies, and coalitions over the seductive ease of unilateralism. But with equal force, an awareness of our responsibility should lead us to defend the liberal world order when it is under attack.

In an older theological tradition of thinking about war and justice, having right intent meant waging war for the sake of building a more just and lasting peace. As Augustine said, echoing Aristotle, “Peace is the end sought for by war. For every man seeks peace by waging war, but no man seeks war by making peace.” We need to analyze our military ventures in the same way. Our war in Afghanistan should culminate with the construction of peace in Afghanistan, not simply the eradication of threats to us.

In his recent book Just War as Christian Discipleship, Daniel M. Bell Jr. develops this expansive ideal of peacemaking as war’s ultimate goal: “If one’s intent in waging war is indeed just, if one really loves one’s enemies and intends to bring the benefits of peace and justice to them, then one will not abandon them when the shooting stops but will be involved in the restoration of a just peace. If one truly desires justice, then one will stay the course and see justice through to completion,” which, Bell explains, “may include a financial commitment, devoting adequate civil affairs and police personnel, as well as perhaps coordinating with nongovernmental organizations in the work of reconstruction.” Others have made much the same argument under the heading of jus post bellum , justice after war. We have a duty to pursue a just peace in the aftermath of war by fostering reconstruction and rebuilding local government.

If we love the Afghans, including the Taliban, as neighbors, our war in their country will aim not only at our security but also at their good. The United States overthrew the Afghan government in 2001 and incurred an obligation to help restore a just peace. We should stay and help the Afghans do the positive work of fostering justice and order in their war-torn land. To put it another way, if the war is a war of self-defense for the Afghans, and not only Americans, it will aim at peace and justice for Afghans as well as for us.

While this argument may resonate with the faithful, it will offend foreign policy realists who believe that morality should play no role in the conduct of the nation’s affairs. But achieving a just peace actually corresponds to, rather than conflicts with, the goals of hard-nosed realists. The Taliban were able to recoup and launch their insurgency in 2005 because the Afghan government remained weak and efforts to rebuild had been paltry. Seth Jones, an analyst with RAND and the foremost American expert on the Taliban insurgency, has argued: “Weak governance is a common precondition of insurgencies. The Afghan government was unable to provide basic services to the population; its security forces were too weak to establish law and order; and too few international forces were available to fill the gap. Afghan insurgent groups took advantage of this anarchic situation.”

Countering an insurgency critically depends on reconstruction and governance reform. Lasting success requires efforts to “foster development of effective governance by a legitimate government,” according to the U.S. Army’s counterinsurgency field manual. Reconstruction and stabilization—the requirements of jus post bellum—are themselves weapons of war in a counterinsurgency. Our obligation to rebuild Afghanistan and our obligation to defend against the Taliban have effectively merged into a single duty. Realists may disagree with the moral framework in which I have cast this argument, but they can agree with the results it guides us toward. To give economic reconstruction and governance assistance in Afghanistan is both a moral duty and a crucial wartime necessity.

An expansive approach to just war thinking also points in the direction of humanitarian intervention, a use of war to punish the wicked and protect the defenseless. This is a controversial way to justify a war. Is it just to invade states for their own good? Can we plausibly claim to be working for justice by launching an aggressive war against regimes we claim are wicked and to defend people against their own government?

Despite the controversy over humanitarian war, the international community has increasingly embraced it in the past fifteen years. Following the worldwide failure to halt the genocide in Rwanda in 1994, the U.N. and the government of Canada put together the Commission on Intervention and State Sovereignty to study when, if ever, intervention is justified. The commission recommended in 2001 that the international community intervene—that it violate sovereignty—to halt large-scale loss of life and ethnic cleansing. A few years later, the criteria were clarified to include genocide, war crimes, and crimes against humanity, as well as ethnic cleansing. The commission rested its argument on the idea that exercising sovereignty entails a “responsibility to protect” the people under one’s care. If a state is unable or unwilling to protect its people, responsibility passes to the international community. The international community unanimously endorsed this norm at the U.N.’s 2005 World Summit.

The modern secular tradition of just war doctrine provides almost no support for the idea of a humanitarian war, because it so strongly emphasizes sovereign immunity and territorial inviolability. However, “responsibility to protect” finds support in the theological underpinnings of the just war tradition. Love of neighbor and the punishment of the wicked—both so prominent in the Bible—lend support to the idea of humanitarian intervention. It’s therefore not surprising that in the early modern era several of the most prominent thinkers who laid the groundwork for modern international law consistently drew upon earlier and more explicitly theological traditions and, in so doing, explicitly addressed and supported the idea of humanitarian intervention.

Writing in the sixteenth century, Francisco de Vitoria challenged the claims Spain made about the justice of her imperial conquest in the New World. Nevertheless, he recognized some legitimate grounds for military intervention. “The tyranny of those who bear rule among the aborigines of America or on the tyrannical laws which work wrong to innocent folk there, such as that which allows the sacrifice of innocent people or the killing in other ways of uncondemned people for cannibalistic purposes,” justifies intervention. If the Indians refused to stop, someone should wage war and change the regime. Punishment can be inflicted for “sins against nature,” Vitoria concludes.

Two generations later, Francisco Suárez made a nuanced argument supporting intervention on behalf of the oppressed. In his view, a prince may justly go to war in response to an injury against himself or against “anyone who has placed himself under the protection of a prince.” A prince may, therefore, respond to injuries not only against himself, but also against “allies and friends.” We may wage war on behalf of others, not, of course, for any reason, but for the sake of a just cause: “It must be understood that such a circumstance justifies war only on condition that the friend himself would be justified in waging war.”

Finally, Hugo Grotius, father of international law, followed Vitoria and Suárez: “It is proper also to observe that kings and those who are possessed of sovereign power have a right to exact punishment not only for injuries affecting immediately themselves or their own subjects, but for gross violations of the law of nature and of nations, done to other states and subjects.” This is so because of “the common tie of one common nature, which alone is sufficient to oblige men to assist each other.”

Grotius, like Suárez, places a limit on this obligation. We are not obligated to risk our national survival for others. But barring that exceptional limitation, intervention is justified to stop abnormal tyranny and wickedness. “Where a Busiris, a Phalaris or a Thracian Diomede provoke their people to despair and resistance by unheard of cruelties, having themselves abandoned all the laws of nature, they lose the rights of independent sovereigns, and can no longer claim the privilege of the law of nations.” Sovereignty does not shield murderous tyranny.

These three writers address only exceptional, grievous, abnormal wickedness and harm inflicted upon fellow human beings: cannibalism, human sacrifice, “unheard-of cruelties,” and “gross violations of the laws of nature.” These acts transcend normal human sin and involve more than the petty injustice or abuse of power found in most states throughout most of history. As Vitoria, Suárez, and Grotius recognize, on rare occasions some governments fall into exceptional evil that justifies intervention. That is what the “responsibility to protect” doctrine claims. It stipulates that some crimes are so appalling, so abnormal, that states lose their normal sovereign immunity and territorial inviolability. It is moralistic, true, but if we cannot condemn génocidaires as wicked, we have larger problems.

Afghanistan has seen some of the worst human suffering and human rights abuses in recent decades. During Afghanistan’s civil wars from 1992 to 2001, warlords at the head of sectarian militias regularly committed war crimes, crimes against humanity, and ethnic cleansing. The Taliban amassed a long record of massacring civilians and targeting the Hazara for ethnic cleansing, notably at Mazar-i-Sharif in 1998, Robatak Pass in 2000, and Yakaolang in 2001. But their crimes were not unique; other militias that are still active today were also guilty of atrocities. Ittehad-e-Islami, for example, was accused of ethnic cleansing against the Hazara during a battle in the West Kabul neighborhood of Afshar in 1993.

If the United States withdraws from Afghanistan precipitously, without ensuring the establishment of a stable government capable of upholding order, civil war will almost certainly erupt. The warlords who fought the civil wars of the 1990s will reestablish their brutal fiefdoms. The Taliban will take power over part or all of Afghanistan, and reprisal murders against supporters of the Karzai government are likely to be widespread and swift—especially against women; the Hazara, Shia, and other religious minorities; and the clans and subclans of Durrani Pashtuns (rivals of the Ghilzai, from whom many of the Taliban leaders are drawn). Failure to prevent this would be a grave and shameful stain on our national character, akin to the slaughter in Vietnam in 1975.

The United States does not have a moral duty to intervene everywhere there is injustice: That would entail a global crusade of never-ending conflict worse than the disease it aimed to cure. The responsibility to protect is rightly limited to exceptional evils. Women, minorities, and political dissidents are oppressed around the world every day, and most of the time the United States is obligated to do exactly nothing. But only most of the time. If the wrong is grave enough, and our ties to the victims close enough, we have an obligation to intervene, all the more so when we are already present with troops on the ground.

In the parable of the Good Samaritan, a traveler on the road to Jericho is waylaid and beaten by thieves. A priest and a Levite pass by the broken and bleeding body before a Samaritan “[goes] to him and bandage[s] his wounds, pouring on oil and wine. Then he put[s] the man on his own donkey, [takes] him to an inn and [takes] care of him.”

Afghanistan is the broken and bleeding traveler in our community of nations, having been waylaid and beaten by the Soviets, the Taliban, and al-Qaeda. Since the Soviet invasion of 1979, Afghanistan has ranked near the bottom of almost every indicator of social, economic, and human development. In 2001, just 13 percent of Afghans had access to safe drinking water. A third or fewer could read or write, and fewer than a million were enrolled in its nearly defunct schools. Seventy percent were undernourished. The average Afghan lived forty-six years; just a third made it to age sixty-five. The gross domestic product per capita was among the worst in the world, and infant mortality the highest. As the Economist rightly observed in January 2001, it was the “worst country on earth.”

There is a general scriptural principle that we should help other people. As the law code of ancient Israel stipulates, “If one of your countrymen becomes poor and is unable to support himself among you, help him as you would an alien or a temporary resident, so he can continue to live among you.” The United States has a responsibility to continue the war and to rebuild Afghanistan—to defend ourselves, to rebuild a country whose government we overthrew, and to defend the oppressed. As a wealthy and powerful nation, we need to keep in mind the words of Jesus: “From everyone who has been given much, much will be demanded; and from the one who has been entrusted with much, much more will be asked.”

I wish it were not so. No one has more incentive to come home than the soldier, especially one who has seen his friends and fellows maimed or killed. I have lived with this war day in and day out for a decade, and I loathe it. As the thousands of soldiers and civilians who have worked for years on Iraq, terrorism, Afghanistan, or Iran know, bearing a burden like this for so long can be dehumanizing and alienating, especially in the face of a disillusioned public and an ignorant media. General Dwight Eisenhower said it best: “I hate war—as only a soldier who has lived it can, only as one who has seen its brutality, its futility, its stupidity.” The only thing that is worse is shirking the claims of justice.

Paul D. Miller is assistant professor of international security affairs at the National Defense University in Washington, D.C. The views expressed here are his own.