Prominent Syria analysts also claimed that Assad supported, even sponsored Islamic State. CNN’s Michael Weiss pushed the line that Assad and Russian President Vladimir Putin would not fight Islamic State and that Syria and Russia were the group’s “unacknowledged air force.” His co‐​author, Hassan Hassan, contended that the Syrian regime must go because “Assad has never fought [Islamic State] before.”

For a while, everywhere one looked, the media was peddling the same narrative. The Daily Beast described Islamic State fighters as “Assad’s henchmen.” The New York Times promoted the idea that “Assad’s forces” have been “aiding” Islamic State by “not only avoiding” the group “but actively seeking to bolster their position.” Time parroted the pro‐​regime‐​change line that “Bashar Assad won’t fight” Islamic State.

But these popular arguments were, to put it mildly, empirically challenged.

The case for regime change in Damascus was reminiscent of the one cooked up for Baghdad in 2003: Interventionists played on American fears by pretending that the strongmen were in direct cahoots with Salafi jihadists (the ultra‐​conservative movement within Sunni Islam). The evidence of Assad sponsoring Islamic State, however, was about as strong as for Saddam Hussein sponsoring Al Qaeda.

As the Syria expert Aymenn Jawad Al‐​Tamimi noted in February 2014, Islamic State “has a record of fighting the regime on multiple fronts, including the Sheikh Said area of Aleppo province, Kwiris military airbase (where an offensive is ongoing under the leadership of muhajireen battalion Suqur al‐​Izz, in coordination with the Green Battalion, [Islamic State] and Jabhat al‐​Nusra), Nubl and Zahara, Brigade 17 airbase in Raqqa province, Tabqa military airport, Qalamoun, Sayyida Zainab, Sakhna in Homs desert, the Qamishli area, and Latakia province. Besides these locations, one should also remember [Islamic State’s] leading role in the capture of Mannagh airbase.”

The notion that Assad “won’t fight” Islamic State was always wrong. The notion that “defeating Islamic State also requires defeating Bashar Assad” was, likewise, always wrong. By now it should be obvious that the Syrian Arab Army has played a role in degrading Islamic State in Syria — not alone, of course, but with Russian and Iranian partners, not to mention the impressive U.S.-led coalition. In marked contrast to pundit expectations, the group’s demise was inversely related to Assad’s power. Islamic State’s fortunes decreased as his influence in the country increased.

Equally contrary to analyst predictions, the group imploded right after external support for the “moderate” rebels dried up. The weakening of the rebels was a major setback for Islamic State because Assad could finally focus his firepower on the group. Fewer weapon shipments into the theater, moreover, meant fewer arms fell into the hands of Salafi jihadists.

How strange, then, that we haven’t heard many pundits acknowledge their mistakes; they’re not itching to atone for having almost forced another regime‐​change mission based on discredited analysis.

The now‐​defunct conventional wisdom was not only stubbornly anti‐​empirical, but unmoored from the political science literature. With few exceptions, international relations scholars seemed content to stand back and watch think tank pundits do the day‐​to‐​day Syria analysis while ignoring the red flags dotting the research landscape.

Some of the best political science research over the past couple of decades finds that militants are less likely to emerge in response to political grievances than from propitious conditions for them to organize. For Islamic State, the “opportunity model” of terrorism was always a better fit than the “grievance model.” After all, this is a group that set up shop in the desert, far away from the Syrian military; preyed on soft targets like the Yazidis who never oppressed the Sunni population; and planted affiliates in countries known not for their anti‐​Sunni government, but the lack of a functioning one.

As in Iraq a decade earlier, regime change in Syria would have created the ultimate power vacuum for Islamic State to flourish.

Moreover, the notion that pumping arms and fighters into Syria would mitigate the unrest is actually the opposite of what study after study has established. The conflict literature makes clear that external support for the opposition tends to exacerbate and extend civil wars, which usually peter out not through power‐​sharing agreements among fighting equals, but when one side — typically, the incumbent — achieves dominance.

The Realist paradigm reminds us that the U.S. need not share the same ideology of a nasty international actor to countenance working with him against a mutual foe. With its sensitivity to overspending and blowback, Realism also emphasizes the dangers of militarily picking foreign governments around the world.

Although the Islamic State’s caliphate is dead, Assad’s war on terrorists in Syria is very much alive. Let’s hope future analysis of this conflict avoids the kind of anti‐​empirical ideological advocacy that helped give rise to Al Qaeda in Iraq and then Islamic State in the first place.