Mounting anti-ISIS offensives

ISIS’ gains and the US intervention in support of Kurdish forces further complicated the mosaic of the Syrian conflict. Assad had lost swathes of territory to ISIS; more importantly, Iraqi and Iranian Shi’a forces left Syria to prop up Baghdad, which exacerbated Assad’s manpower shortages and helped shift the momentum back towards the armed opposition.[1] Facilitated by a Turkish-Saudi agreement, an Islamist armed coalition, Jaish al-Fateh, coordinated with Nusra to take control of Idlib in March 2015.[2] It was the first time the city had come under the control of opposition forces, and by June 2015, they controlled all of Idlib province.

But despite their success, infighting between rebel forces continued. Nusra, which had also been targeted by US airstrikes since 2014, on various occasions fought against US-backed opposition groups; in late 2015, Nusra split with Ahrar al-Sham over the application of Shari’a in opposition-held territories and left the Jaish al-Fateh coalition.[3] The next year, Nusra changed its name (eventually becoming Ha’yat Tahrir al-Sham, or HTS, its current form) and announced it had ended its relationship with al-Qaida, although critics questioned the authenticity of the split, arguing that it continued to receive strategic and operational guidance from al-Qaida.[4]

Following several military setbacks for pro-Assad forces and the mounting losses in Idlib, Russia decided to intervene militarily in September 2015. Russian President Vladimir Putin took the decision to ensure the survival of Assad and prevent regime collapse, but this decision also provided geostrategic gains to Russia, which had found itself increasingly isolated following the 2014 Ukraine/Crimea crisis. Although there was a risk of ISIS taking control of Damascus should Assad fall, the narrative that Russian support was delivered solely to fight ISIS did not hold up: Russia’s campaign was primarily aimed at forces other than ISIS in northern areas around Hama and Idlib, as well as in Dera’a in southwestern Syria.[5] As a result of the Russian intervention, Assad was able to make major gains in early 2016 that shifted momentum away from the opposition and eventually led to a series of poorly observed ceasefires and cessations in hostilities that favoured Assad in the medium term (and were repeatedly violated by his forces under the pretext of targeting Nusra). Around Aleppo, ISIS was able to move in after Russia repeatedly bombarded opposition forces.[6]

In November 2016, the SDF—a US-backed umbrella force that included Arab units but consisted primarily of Kurdish YPG fighters—announced they would move on Raqqa.[7]  Under US President Donald Trump, who took office in January 2017, the US took several additional steps intended to target ISIS, including providing lethal support to the SDF.[8] By early 2017, the SDF had surrounded around four thousand ISIS fighters in Raqqa; in parallel, Iraqi forces were moving towards retaking Mosul—a goal that would finally be achieved in July that year. The fall of Raqqa followed in October 2017, dealing a blow to the “caliphate” from which it would never recover—although it came with heavy losses among the SDF and even heavier losses among the city’s civilian population.[9] Meanwhile, Assad’s forces, supported by Iranian-backed groups and other allied militias, retook Deir Ezzor and large areas of eastern Syria, taking advantage of ISIS’ losses. The remaining ISIS fighters retreated to the border areas around al-Bukamal. ISIS was near defeat, but the Turkish invasion of Afrin in early 2018 drew Kurdish forces away from the anti-ISIS campaign. As a result, it took until February 2019 for the SDF to finally defeat ISIS in its last stronghold, Baghouz Fawqani. The geographical “caliphate” had ceased to exist. ISIS looked like a spent force. It had lost control of all its territory against the overwhelming force of multiple enemies on several simultaneous fronts. While “caliph” Baghdadi managed to escape from Baghouz, it would not be long until he too would meet his end, self-detonating a suicide vest during a US raid in Idlib province in October 2019.[10] Idlib remained under the control of HTS and the ISIS-affiliate-turned-rival maintained between 12,000 to 15,000 fighters in the area.[11]

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