John Paul II defines terrorism as “intention to kill people and destroy property indiscriminately and to create a climate of terror and insecurity, often including the taking of hostages” (Solicitudo Rei Socialis, #24).
And isn’t intentional killing—the direct destruction of the lives of any who fail to submit to the goal of a world-wide Islamic Caliphate—precisely what we see in the militant acts of ISIL?  As such, their acts of killing are murder. They deliberately violate the absolute natural law norm that prohibits the intentional killing of human beings. 
To grasp the moral difference between ISIL’s intentional acts of killing and the killing of ISIL terrorists by American armed forces within a just war, we need to do two things. First, review how the constellation of America’s declaration of war with ISIL  creates an ethos on the ground which dictates a just intention. In other words, America’s use of armed force in the presence of a just authority, just cause, last resort, and serious prospects of success is not the immoral act of intentional killing (i.e., murder) but the unintended effect of another action altogether: the morally good act of collective self-defense in the pursuit of justice. In short, what President Obama wills, what he intends, both in the enactment and execution of the war with ISIL, is not the killing of ISIL, but the use of proportionate military force against them to defend the collective lives and freedoms of Americans.
Second, we need to consider why it is critical for US civilians, especially news commentators, journalists, and political pundits, to both appreciate and appropriate the just intentionality of the enactment and execution of the war with ISIL.
Part One: The moral constellation of America’s declaration of war with ISIL
The US decision to go to war with ISIL has been justly enacted by the president.
Legitimately-constituted political authorities, because they are responsible for the common good, have the right and, therefore, the duty to endorse the use of lethal force against unjust aggressors for the sake of justice, that is, to defend the endangered lives, freedom, and dignity of their citizenry. Given that justice is the foundation of love, Thomas Aquinas discusses just war, or the collective act of self-defense, under the virtue of charity (Summa Theologiae II-II, 41, a.1, ad. 3 and 64, a. 7). Paul Ramsey argues discernment of the justice of a probable war is recognition of the public meaning of the second great commandment. And Augustine asserts failure to use armed force to address a wrong that can only be corrected with violence is a sin, while the defense of one’s self or others could be a necessity, especially when authorized by a legitimate authority.
In his public statement of September 10, 2014, President Obama announced that “America will lead a broad coalition to roll back this terrorist threat.” As part of his comprehensive strategy he ordered the men and women of our military “to take targeted action against ISIL to stop its advances” through, first, “a systematic campaign of air strikes” and, second, American troop support of Iraqi and Kurdish forces “with training, intelligence, and equipment.” The president sanctioned the use of deadly force against ISIL for the sake of what he describes as his “highest priority”: to secure the lives and liberty of Americans threatened by these terrorists.
The US decision to go to war with ISIL has been justly enacted by the president and has a just cause.
President Obama made it clear he is going to war for one reason and one reason only: to defend Americans, our allies, and religious minorities in the Middle East whose lives, rights, and dignity are in imminent danger from the aggressive threat of ISIL. As such, his cause for war is just. It fulfills exactly the just cause criterion stipulated by the United States Catholic Conference: “Force may be used only to correct a grave, public evil, i.e., aggression or massive violation of the basic human rights of whole populations.” Or the just cause requisite of the Catechism of the Catholic Church: “the damage inflicted by the aggressor on the nation or community of nations must be lasting, grave, and certain” (CCC #2309).
Of course, a country like the US cannot simply claim to have a just cause. It must also be able to prove that ISIL’s wrongs rise to the order of an injustice for which war is the only proper redress.
Thanks to their barbarous bravado, the task of verifying the persistence, gravity, and certainty of ISIL’s acts of terror is only a matter of believing our eyes. First (if we can stomach it), we need only to watch the video accounts of their monstrous beheadings of innocent journalists and humanitarians and their mass executions of Shiite Muslims, Yazidis, and Christians. Second, we have only to read reports from social media and journalists detailing ISIL’s intentional killing of innocent children and adults, their raping and enslavement of minority women, and their intentional theft and destruction of private and state property. Finally, proof of their aggression is only a matter of believing our ears—heeding public pronouncements like that of “Jihadi John” who, while holding the head of US citizen Peter Kassig, decreed: “To Obama, the dog of Rome. Today we are slaughtering the soldiers of Bashar and tomorrow we will be slaughtering your soldiers and, with Allah’s permission, we will break this final and last crusade and the Islamic State will soon…begin to slaughter your people on your streets.”
The US decision to go to war with ISIL has been justly enacted by the president, has a just cause, and is the last resort.
A declaration of war is permissible only after every other means—economic, political, or diplomatic—has been tried and “shown to be impractical or ineffective” (CCC #2309). There appears to be a general consensus within the Obama administration and the Congress regarding the futility of pursuing negotiations with ISIL. Since they have demonstrated their quintessential irrationality time and again, reasoning with them is a literal impossibility. But that aside, ISIL also lacks official statehood: they possess no ambassadors and receive none from other nations. That excludes the possibility of diplomatic discussion. They lack an organized government with a concomitant financial and constitutional infrastructure. That eliminates the possibility of economic or political sanctions.
Realistically, war is the only and best means to stop ISIL, to prevent them from carrying out their intentional acts of killing and rape, plunder and pilfering.
The US decision to go to war with ISIL has been justly enacted by the president, has a just cause, is the last resort, and has serious prospects of success.
The School of Salamanca, 16th-17th century Spanish commentators on the works of medieval philosophers, expanded Aquinas’ just war theory by insisting that, since war is one of the worst evils suffered by mankind, it ought to be resorted to only to prevent an even greater evil. Hence, they considered a war of self-defense to be just only if it had a reasonable possibility of success.
This criterion was eventually incorporated within the Church’s just war tradition and is clearly stated in the Catechism of the Catholic Church, paragraph 2309: “The strict conditions for legitimate defense by military force require rigorous consideration. The gravity of such a decision makes it subject to rigorous conditions of moral legitimacy.” And the moral criteria enumerated by the catechism include not only those already discussed here but also that “there must be serious prospects of success” and that “the use of arms must not produce evils and disorders graver than the evil to be eliminated.” In other words, arms may not be used in a futile cause or when disproportionate measures such as nuclear or chemical warfare are necessary to achieving success.
First, I think it is reasonable to predict, given the sophistication of American air and ground power, especially if we allow our troops to fight alongside Iraqi forces, the anticipated benefit of waging a war with ISIL—eliminating its ability to carry out its indiscriminate acts of murder, plunder, rape, and terror within and far beyond the Middle East—is proportionate to or greater than its unintended bad consequences. Second, especially when we consider that the radical Islamist position of “convert, die, or be enslaved” would never be imposed by the American-led coalition on defeated members of ISIL, the answer to the question—would a greater evil result from the war with ISIL than that prevented?—is “no.”
Since the US decision to go to war with ISIL has been justly enacted by the president, has a just cause, is the last resort, and has serious prospects of success, the intentionality of the act of killing in the war with ISIL is also just.
Not all killing is murder. Witness the act of personal self-defense and the act of killing in war (collective self-defense). Since the Ferguson, Missouri case is fresh in everyone’s memory, let’s use it to analyze the act of personal self-defense. The grand jury ruling in that case concluded that although Officer Darren Wilson killed (physically caused the death of) Michael Brown, he did not murder him; the grand jury found he was not guilty of homicide. The grand jury’s decision of self-defense—a confirmation of Wilson’s personal testimony—means this: Mr. Wilson’s act of killing, although physically direct, was not a morally direct or intentional act of killing. Stated differently, since evidence revealed that Brown charged at Wilson in an act of physical assault, the intentionality of Wilson’s act of killing was not the use of force to kill Brown, but the proportionate use of force to save his life from Brown’s unjust aggression. Therefore, the grand jury determined that Wilson’s act of killing was neither a violation of, nor an exception to, the absolute prohibition of intentional killing or murder. It was the unintended effect of another act altogether, one whose permissibility falls under the norm of legitimate self-defense, the right “to render an unjust aggressor unable to inflict harm” (CCC #2321). According to the grand jury’s findings, the death or physical act of killing Michael Brown was praeter intentionem–outside officer Wilson’s intent—not something Wilson willed (deliberately chose to do) but an unintended consequence or effect of what he did will or intend, namely, to preserve his own life from Brown’s aggression.
The same ethical calculus can be applied to an act of collective self-defense, or to the act of killing in war. Once the conditions of the declaration of a just war with ISIL were met—just authority, just cause, last resort, serious prospects of success—these ethical facts on the ground collaborated to define and activate the just intentionality  of President Obama’s declaration of war. His decision to use lethal force is neither a violation of, nor an exception to, the absolute prohibition “you shall not kill,” but the unintended consequence of another act altogether, one whose permissibility falls under the norm that, once all peace efforts fail, “governments cannot be denied the right of lawful self-defense” (CCC #2308). In other words, the moral object of the president’s decision—to use lethal force against the unjust aggression of ISIL (the means) for the sake of defending the lives, dignity, and freedom of American citizens (the end)—is a just act of collective self-defense, an act of reclaiming justice and peace for all those whose lives, liberty, and dignity are already, or will be, imperiled by ISIL’s aggression. The killing of ISIL terrorists, then, is an unintended effect of the president’s intentional act of collective self-defense.
American military who serve at the pleasure of the president are duty-bound to carry out his same just intention as they execute the war (CCC #2310). With their wills directed to defense of their country and its citizenry, American forces who kill ISIL members, whether through bombing, through drone-guided missiles, or through hand-to-hand combat, are not committing moral acts of intentional killing. Causing the death of ISIL terrorists is praeter intentionem—outside their intent or will, that is, not something American servicemen will or intend (deliberately choose to do) but an unintended consequence or effect of what they intend to do: to use lethal force against the unjust aggression of ISIL in the just pursuit of defending American lives, liberty, and dignity.
Part Two: Why American civilians should also inform their wills according to the just war tradition
It follows from everything said that, to the extent our American forces maintain a just intentionality in executing their offensive, killing within the ISIL war will not be murder, will not be fighting terrorism with terrorism but will, instead, be the unintended consequence of the just pursuit of an act of collective self-defense.
The onus of helping servicemen and women continue to shape their wills according to the just intentionality articulated by their commander-in-chief rests squarely on the shoulders of those standing behind the influential podiums of print, radio, TV, and Internet news outlets. Following ISIL’s beheading of two Americans, inflammatory reactions from some of our media pundits—“Let’s kill those cockroaches,” or, “Let’s blow the hell out of them”—though understandable in light of the horror of the moment, tend only to encourage our troops in Iraq to direct their wills to intentional killing, to fighting terrorism with terrorism, to answering the murderous acts of ISIL with a like thirst for vengeance.
Such incendiary penchants from the mouths and keyboards of social and news media, diametrically opposed as they are to the just intentionality of the act of collective self-defense, have real potential to corrupt and skew the minds and wills of our American forces in Syria and Iraq.
It is prudent, therefore, for all Americans—politicians, members of the media, civilians—to inform their will in respect to the morality of killing in war according to the right reason of the just war tradition. With this extra-military reinforcement of a just intention, we can be more confident that any killing of ISIL members or, God forbid, of innocent civilians, whether through US bombing, ground combat, assassinations, or drone-directed missiles, will not constitute murder, i.e., the intention to kill another human being, but the unintended (and regrettable) consequence of a just act of American self-defense.
 The abbreviation ISIL stands for Islamic State of Iraq and the Levant. The Levant refers to a large region including areas of Cyprus, Turkey, Israel, Jordan, Lebanon, Syria, and Palestine. The same terrorist group is also referred to as ISIS: the Islamic State of Iraq and al-Sham or the Islamic State of Iraq and Syria.
 The Catechism of the Catholic Church (#2268) states clearly: “The fifth commandment [‘You shall not kill.’ (Ex. 20:13; Dt. 5:17)] forbids direct and intentional killing as gravely sinful. The murderer and those who cooperate voluntarily in murder commit a sin that cries out to heaven for vengeance.” In Mt. 5:21-22, Jesus expands the Old Testament notion of murder to also include thoughts and words of anger and vengeance: “You have heard that it was said to the men of old, ‘You shall not kill: and whoever kills shall be liable to judgment.’ But I say to you that every one who is angry with his brother shall be liable to judgment.”
 As George Weigel points out: The just war tradition is not “an algebra[ic formula] that provides custom-made, clear-cut answers under all circumstances. Rather, it is a kind of ethical calculus, in which moral reasoning and rigorous empirical analysis are meant to work together, in order to provide guidance to public authorities on whom responsibilities of decision-making fall.”(“The Catholic Difference: Getting ‘Just-War’ Straight”; Zenit published this article on October 13, 2001 under the heading “George Weigel on Just-War Principles.”)
 In his enactment address, President Obama directly appeals to Americans to support him in carrying US leadership forward: “America, our endless blessings bestow an enduring burden. But as Americans, we welcome our responsibility to lead. From Europe to Asia, from the far reaches of Africa to war-torn capitals of the Middle East, we stand for freedom, for justice, for dignity. These are values that have guided our nation since its founding.” In other words, the US military offensive was not only being fought to defend America from the barbaric aggression of ISIL but to protect all nations and religious minorities who were similarly and even more imminently threatened.
 In “Just War Theory,” Jon Darbolo makes the important distinction that the right political authority to initiate war is one who leads a political system “that allows distinctions of justice.” Hence, war declarations from dictators (e.g., Hitler’s regime) or deceptive military actions (e.g., the 1968 US bombing of Cambodia) are typically considered violations of this criterion.
 City of God, Book I, Chapter 21: “And, accordingly, 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.’”
 ISIL’s reference to the “last crusade” suggests their thirst for vengeance stretches all the way back to Muslim defeats suffered in the 11th century: In 1098 Crusaders wrested Nicaea and Antioch from Muslim dominance and returned them to Christian rule, and in 1099 the same Christian forces conquered the previously held Muslim stronghold of Jerusalem and began building Palestine into a Christian nation.
 The grand jury concluded Officer Wilson acted within the limits of the lethal-force law. Eyder Peralta and Krishnadev Calamur, “Ferguson Documents: How the Grand Jury Reached a Decision,” NPR, November 26, 2014.
 An example of an unjust intention for going to war would be for material gain or maintaining economies. President Obama, in his declaration of war with ISIL, held up their motives as an example of an unjust intentionality: “exploit[ing] grievances for their own gain,” taking “advantage of sectarian strife and Syria’s civil war to gain territory on both sides of the Iraqi-Syrian border.” ISIL has also profited financially from confiscated oil fields and land, all of which were once the property of the people of Syria and Iraq.
 Although space does not allow full discussion of post-bellum just war criteria in respect to ISIL, Germain Grisez succinctly summarizes them: “Even when carried out within proper limits, deadly force against persons cannot be an adequate response to terrorism. A sound response must also include a very serious and sincere effort to improve relationships with less radical members of the group whose interests the terrorists are trying to promote by their bad means. That serious effort at reconciliation must be implemented by economic and political action designed to mitigate suffering and reduce hatred” (“Renowned Moral Theologian Weighs in on Anti-Terrorism,” Zenit, September 29, 2001). There already is ample evidence on the part of the Obama administration to include more moderate Muslims in the fight against ISIL, to enlist their public condemnation of radical Islamic groups like ISIL, and to solicit international support from our allies in the war against ISIL.
 Although President Obama’s declaration of military force against ISIL stipulated American troops on the ground would only train and act as advisory units for the Iraqi ground forces, it now appears likely that American troops will also be actively engaged in ground warfare.