The United States developed—or further developed—a strategy called “by, with, and through” for its successful military campaign from 2014 to 2019 against the Islamic State, or ISIS. Under this strategy, the United States worked with local forces by providing advice, supplies, and intelligence, and carrying out airstrikes. But the locals were expected to take almost all of the casualties. And, indeed, they did: tens of thousands of people were killed in the war, but only twenty of them were American service personnel.

Key to the success of the strategy was the willingness of the locals to fight and die for the cause. This quality is difficult to inspire or fabricate, but it helps greatly if the enemy, as in the case of ISIS, is taken to present a threat that is genocidal or existential to the locals.

For all the success, however, it seems possible that civilian deaths would have been far lower if ISIS fighters, many of them disillusioned and fundamentally muddled, had been allowed to flee the fray.

The Rise of “By, With, and Through”

Degrade and Destroy: The Inside Story of the War Against the Islamic State from Barack Obama to Donald Trump, an impressive book by Michael Gordon, a top military reporter for the Wall Street Journal, can help to guide the discussion. The book focuses primarily and in considerable depth on the American contribution to the campaign, but it does not deal very much with the fighting qualities of ISIS—an omission that has come with analytical consequences, as will be seen. Nonetheless, it is highly useful in assessing the development of the strategy that defeated ISIS.

Although Gordon concludes that the “by, with, and through” strategy constitutes a “new way of war,” it is not clear that the strategy is all that new. Gordon himself espies “elements” of it in earlier interventions, but in many respects, it was fully in view in the American (and European) approach to civil wars in Bosnia and Croatia in the early 1990s. The outside interveners were willing to supply and advise one side in those conflicts and even to apply some focused bombing. But U.S. troops were sent to police the situation only in 1995 after the wars had been substantially settled—when the military environment had become “permissive,” as it was put at the time by President Bill Clinton and others. Helpful to the success of the mission was the fact that the opposing Serb forces were substantially incompetent and criminalized.

Something similar could be seen in U.S. strategy in the last years of the Vietnam War two decades earlier. Sapped by declining popular support for the war at home, the U.S. contribution had been reduced to a supporting role by 1971, while the South Vietnamese forces America had trained were expected to bear the brunt of any ground fighting. In 1972, North Vietnam launched a major offensive, and for a while, it looked like South Vietnam’s military would fold. However, some elements did hang on, blunting the offensive. When that was obvious, the United States re-entered combat, but mainly with airpower, and the combined effort defeated the offensive. But three years later, when the North launched another offensive, the ill-led South Vietnamese military collapsed, and the United States mainly stood back and withdrew its personnel, watching as the North took over and handed the United States the greatest debacle in its foreign policy history—something it accepted with remarkable equanimity as it turned out.

Foreign policy analyst David Ignatius argues that the United States military may well have found a “winning combination” in its war against ISIS. However, as the Vietnam experience suggests, it needs local forces that are prepared to do the fighting and dying. Indeed, in a broader comparative study, Stephen Biddle and his colleagues conclude that security force assistance works best, and perhaps only, if the locals are convinced they face a mind-concentratingly existential challenge. Otherwise, their interests are likely to depart considerably from those assisting them.

“By, With, and Through” in Iraq and Syria

A problem is that a willingness by the locals cannot readily be created by U.S. efforts. Because of its focus on the Americans, Gordon’s book tends to underplay the dynamic.

To begin with, the United States spent $20 billion over a decade to create defense forces in Iraq. However, confused and corruption-ridden, these forces simply fell apart when challenged by ISIS fighters in 2014, abandoning territory and weaponry to ISIS even though the defending forces often greatly outnumbered the challengers.

But there was soon a remarkable transformation: effective forces in opposition to ISIS emerged among the locals. They came not only from the Iraqi army but also from various militia and paramilitary groups, especially Kurdish ones. They often squabbled and, as Gordon extensively documents, a central U.S. mission was to get them to coordinate their efforts. But all were in agreement on the need to extinguish ISIS and to risk death in the process.

However, although this change was likely bolstered by the American commitment, it was caused not so much by that as by local revulsion at the vicious and genocidal tactics and goals of ISIS, which, as Daniel Byman puts it, had a “genius at making enemies.” A poll conducted in Iraq in January 2016 found that fully 99 percent of Shiites and 95 percent of Sunnis expressed opposition to ISIS. Spines had become steeled by its staged beheadings of hostages, summary executions of prisoners, and rape and enslavement of female captives. For example, in 2014, ISIS massacred some 1,700 unarmed captured Shia military cadets by shooting, beheading, and choking them, triumphantly web-casting videos of the event. This mind-concentrating episode is mentioned only in passing by Gordon. But, as one ISIS opponent puts it bluntly in the film City of Ghosts, the conclusion for many was “either we will win, or they will kill us all.”

In addition, the U.S. strategy against ISIS was aided by the fact that Americans came to believe that the enemy presented a direct threat to the United States—another element that is substantially missing from Gordon’s narrative. This stemmed from the vicious group’s ultimate idiocy: staging and webcasting beheadings of defenseless American and Western hostages in the late summer and early fall of 2014. Only 17 percent of the American public had advocated sending ground troops to fight ISIS after its successful routs earlier in the year—it seemed to be yet another incomprehensible civil conflict among Iraqi factions. However, the beheadings—tragic and disgusting, but hardly of the order of the magnitude of destruction wreaked on 9/11—boosted support to over 40 percent, and that went even higher later. A poll conducted in 2016 asked the 83 percent of its respondents who closely followed news about ISIS whether the group presented “a serious threat to the existence or survival of the U.S.” Fully 77 percent agreed, more than two-thirds of them strongly.

Reducing Civilian Casualties

Because of its focus on American policy and strategy, Gordon’s book says little about the inner workings and machinations of ISIS, and this is sometimes unfortunate. The issue is especially relevant to some brief suggestions at the end of the book that efforts should be made to improve the strategy to reduce civilian casualties. As he points out, U.S. strategy, particularly as put forward by Secretary of Defense General Jim Mattis, was focused on “annihilating” ISIS. As a result, sieges of ISIS forces often made the fighters cornered rats and did not allow them an escape route. This led to situations such as the one in which an American bomb blew up a building housing two ISIS snipers, killing 105 civilians in the process. But sometimes, local commanders did allow for escape routes, and evidence in the book suggests that this may have saved many civilian lives.

As Gordon points out, the concern was that if ISIS fighters were allowed to escape, they would be free to rejoin the battle elsewhere. But this concern seems to have been based on an overestimate of their capacities and dedication.

In fact, after its startlingly easy advances of 2014, in which Iraqi defenders mainly fled, ISIS did not show much dedicated military tenacity. Some of this was evident even at the time when the group announced in 2014 that it was “ready to burn 10,000 fighters” in one fight but abandoned the field after the loss of a few hundred. In late 2015, it launched three badly-coordinated offensives in northern Iraq that included “armored bulldozers,” but all were readily beaten back.

Frontline commanders observed of ISIS that “they don’t fight. They just send car bombs and then run away. Their leaders are begging them to fight, but they answer that it is a lost cause. They refuse to obey and run away.” Increasingly, ISIS sought to ferret out informants within the ranks, some of them alienated by sharp cuts in salaries, executing them by such methods as dropping them into vats of acid. In defense, ISIS seems primarily to have relied not on well-organized military operations, but on planting booby traps, using snipers, and cowering among civilians. For example, to maintain its human shield, ISIS murdered hundreds of civilians who tried to escape, sometimes hanging the corpses from electrical pylons as a warning.