Only two years ago, hardly anyone outside of a small community of terrorism analysts and Syria watchers had heard of the Islamic State of Iraq and Syria. Yet now, after the terror attacks in Paris, much of the world is focused on the group. And many are asking: How did this group come so far? How did the world, and to at least some degree the United States, let this happen?
Fred Hof, for six crucial months in 2012, played a lead role in shaping US policy toward the Syrian civil war that helped give rise to ISIS. He was the Obama administration's special adviser for the transition in Syria from March to September that year, and now is a resident senior fellow with the Atlantic Council's Rafik Hariri Center for the Middle East. I got in touch with Hof over email to ask him about ISIS and its rise.
The two biggest causes of ISIS's rise, Hof said, are sectarianism in Iraq and Bashar al-Assad's vicious actions in Syria. "ISIS is a vacuum filler," he wrote. But he singled out some outside actors as well, including the US. "The stupidity" of some individuals in nearby states like Saudi Arabia and Qatar who funded ISIS is "impossible to describe adequately in any known language," he said. And on President Obama's current efforts on fighting ISIS: "I truly don't get it."
What follows is our emailed exchange, edited lightly for length and clarity.
Zack Beauchamp: The American public mostly stopped paying attention to al-Qaeda in Iraq [AQI], the group that would eventually become ISIS, around 2009. Then five years later, in 2014, the group marched across Iraq. What were the key factors, in those intervening years, that allowed ISIS to grow so strong?
Fred Hof: Between 2009 and 2014, ISIS — the marriage of AQI and hardcore Saddam Hussein Baathists — was resurrected thanks to crises in political illegitimacy in both Iraq and Syria.
In Iraq, it was [Iraqi Prime Minister] Nouri al-Maliki's Iran-abetted sectarianism that thoroughly alienated and disenfranchised Iraq's Sunni Arabs. In Syria, it was Bashar al-Assad's Iranian-supported attempt to suppress political dissent with overwhelming military force that created a vacuum in eastern Syria that ISIS was able to fill by moving in from Iraq. ISIS is a vacuum filler, and there were political legitimacy vacuums in both places.
Zack Beauchamp: During that same time period, which country was a more important incubator for ISIS: Iraq or Syria?
Fred Hof: Iraq was the essential incubator. If ISIS has not been resurrected in Iraq, eastern Syria today would be in the hands of various nationalist rebel forces.
Raw political sectarianism in Iraq was the main causal factor [in ISIS's rise], overcoming the positive effects of the  American surge and its outreach to Sunni Arab Iraqis. In Syria it was a civil armed conflict caused by Assad regime violence. Assad lost control of the east, Syrian rebels were too weak and disunited to hold it, and ISIS moved in, establishing its headquarters in Raqqa.
Zack Beauchamp: Let's focus on the Syria story for a second. What events, policy decisions, etc., were most responsible for ISIS's growth inside Syria?
Fred Hof: The rise of ISIS was both foreseeable and intended in the context of Assad regime policies toward political dissent.
From the beginning of the Syrian uprising, Assad characterized the opposition to him as terrorist in nature. Early on, he emptied his prisons of Islamist extremists in an effort to pollute the opposition with sectarianism. Ultimately he succeeded in militarizing the uprising [forcing protesters to take up arms to defend themselves], but when he did, he all but lost eastern Syria. This created a vacuum that ISIS, coming in from Iraq, was able to fill.
For Assad, this was a welcome development. He had supported AQI for some eight years, so he was not unfamiliar with the organization. And its arrival in Syria gave substance to his story that it was him versus international terrorism. Today he offers himself as the alternative to ISIS, and is fully supported in this incredible position by Russia and Iran.
Zack Beauchamp: What about other Middle Eastern powers? You hear a lot about the role that money coming in from Gulf states, such as Saudi Arabia and Qatar, played in ISIS's rise during the early parts of the Syrian war.
Fred Hof: Assad's policies inspired some very wealthy Gulf Arabs to support financially a wide spectrum of sectarian responses to the brutality of the regime. This financial support was important to the rise of ISIS and the Nusra Front [al-Qaeda's Syria franchise] in particular.
In reality, it was a service of incalculable value to the Assad regime: It enabled him to say — albeit inaccurately — that he was the alternative to terrorism and sectarianism. The stupidity of private donors from the Gulf in supporting Assad's thesis is impossible to describe adequately in any known language.
Zack Beauchamp: Could the United States have prevented ISIS from rising — or at least from growing so strong? If so, how?
Fred Hof: In mid-2012, President Obama's key national security officials — [Secretary of State Hillary] Clinton, [Secretary of Defense Leon] Panetta, [CIA Director David] Petraeus, and [Chair of the Joint Chiefs of Staff Martin] Dempsey — all recommended a robust training and equipping effort designed to unite and strengthen nationalist anti-Assad rebels. One of the justifications for the recommendation was that they were beginning to see the rise of al-Qaeda-related elements in Syria.
Had that recommendation been accepted and then implemented properly, the ISIS presence in Syria would not be what it is today. Had the US been able to offer Syrian civilians a modicum of protection from Assad regime collective punishment — barrel bombs and all the rest — a major ISIS recruiting tool around the world and inside Syria could have been diluted and even neutralized.
Zack Beauchamp: At this point, today, is it possible today to defeat ISIS without also solving the conflict between Assad and the leading rebel groups?
Fred Hof: If the US were to organize and lead a coalition of the willing to inject professional ground forces into eastern Syria capable of closing with ISIS and killing it, then, yes: ISIS could be defeated in Syria without a political settlement between Assad and his enemies.
All that's been lacking in the near-term battle against ISIS — both in Syria and Iraq — is capable ground combat components of a military effort that has been largely aerial in nature. In the long term, ISIS will be destroyed only when there is legitimate governance in both Iraq and Syria.
Zack Beauchamp: In your estimation, what are the most flawed parts of the US's current strategy?
Fred Hof: In the wake of the Paris abomination I would have bet good money that President Obama would finally direct an attempt to build a coalition of regional and European states to put ground forces into Syria capable of defeating ISIS. Taking down the organization's headquarters and logistical lines into Iraq would have a very positive impact on the battle next door. Within Syria the nationalist opposition could be given the opportunity to bring decent governance to a large chunk of the country.
At present the ground component of the war in Syria is totally inadequate. Kurdish militiamen are good but are focused on securing and defending Kurdish areas. Trying to suppress ISIS mainly through the air is like one hand clapping. Yet for some reason President Obama shrinks from coalition building, saying that the only alternative to what he's doing now is putting 50,000 American troops into Syria. I truly don't get it.