Islamic State in Iraq and Syria

Islamic State in Iraq and Syria (ISIS), transnational jihad movement that has orchestrated or inspired numerous terrorist attacks around the world, including the Paris attacks of 2015, the Brussels bombings of 2016, the Orlando shooting of 2016, and the New Orleans attack of 2025. Certain affiliates, most notably Islamic State–Khorasan Province (ISKP; also called ISIS-K) in Afghanistan and Islamic State–West Africa Province (ISWAP; also called ISIS-WA or Boko Haram) in Nigeria, are sometimes referred to as “ISIS,” despite having a separate leadership base outside of Iraq and Syria.

The original organization grew out of an insurgency by Sunni Iraqis during the Iraq War (2003–11), which had taken on sectarian dimensions. It originated as an affiliate of al-Qaeda but began acting autonomously in 2013, leading al-Qaeda to disavow the affiliate in early 2014. Meanwhile, the power vacuum in Syria amid the Syrian Civil War (2011– ) allowed the group to expand into the eastern portion of the country. After making significant territorial gains in Iraq in June 2014, ISIS proclaimed the establishment of a caliphate led by the group’s leader, Abu Bakr al-Baghdadi. International efforts to defeat the group led to its decline, and both the Iraqi and Syrian governments considered ISIS effectively defeated in their countries by November 2017, though ISIS remained active well after its defeat and began seeing a resurgence in Syria in 2024.

Roots in Iraq

ISIS has its origins in the Iraq War of 2003–11. Al-Qaeda in Iraq (AQI), its direct precursor, was one of the central actors in a larger Sunni insurgency against the Iraqi government and foreign occupying forces. Under the leadership of Abu Musab al-Zarqawi, AQI was responsible for some of the most spectacular and brutal attacks of that conflict. Shortly after Zarqawi’s death in 2006, the group combined with several smaller militant groups and rebranded itself as the Islamic State of Iraq (ISI), a change that reflected the group’s efforts to expand its appeal as well as its ambition to obtain universal leadership of the country’s Islamic militants. The group’s activities were greatly diminished when many of the Sunni tribes of western Iraq turned against it, however, beginning in 2007. The reasons for that reversal included the ISI fighters’ harsh treatment of the populace in areas under their control and a new counterinsurgency strategy that paid Sunni tribal leaders not to participate in attacks. AQI/ISI was also weakened by the loss of several of its senior leaders in attacks by U.S. and Iraqi forces. In 2010 leadership of the group was taken over by Abu Bakr al-Baghdadi (birth name: Ibrāhīm ʿAwwād Ibrāhīm ʿAlī al-Badrī al-Sāmarrāʾī), who was able to elude U.S. and Iraqi forces until 2019.

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The strongly sectarian cast of Iraqi politics at the time, and specifically the repression of Sunnis carried out by the administration of Prime Minister Nouri al-Maliki under the guise of fighting al-Qaeda and remnants of the Baʿath regime, ensured that the Sunni areas of western Iraq remained fertile ground for extremism. The sharpening of Sunni discontent, coupled with the gradual withdrawal of foreign troops, allowed AQI/ISI to make a recovery beginning about 2011, and bombings by Sunni militants once again became a frequent occurrence.

The Syrian theater

The Syrian Civil War, which began as an uprising against the regime of Pres. Bashar al-Assad in early 2011, provided new opportunities for AQI/ISI, whose fighters could easily cross from Iraq into eastern Syria. By late 2012 the assortment of mostly secular rebel groups that had been the mainstay of the armed opposition appeared to be weakening as a result of infighting and exhaustion, and Islamist forces took on a more prominent role. Those included the Islamic Front, an alliance of local Islamist rebel groups; the Nusrah Front, a network aligned with the central faction of al-Qaeda led by Ayman al-Zawahiri; and fighters loyal to Abu Bakr al-Baghdadi. In April 2013 Baghdadi announced his intention to combine his forces in Iraq and Syria with the Nusrah Front under the name Islamic State in Iraq and Al-Shām (ISIS; Shām, a term referring roughly to the Levant, is often translated as “Syria”). The merger was rejected by the Nusrah Front; the split put the two groups in competition, especially for recruits, and eventually resulted in open fighting. (The Nusrah Front later became the leading faction of Hayat Tahrir al-Sham, which in 2024 toppled the Syrian government of Bashar al-Assad.)

ISIS quickly established a zone of exclusive authority in eastern areas of the country that had long ago slipped out of the government’s control. In that zone, which centered on the eastern city of Al-Raqqah, it imposed a strict version of Islamic law. The group’s propaganda, which emphasized its successes in battle and its brutal treatment of enemies and those it deemed to be violators of Islamic law, was thought to have attracted significant numbers of radicalized recruits from outside Iraq and Syria, although the precise numbers remained uncertain. ISIS also seized critical pieces of infrastructure in eastern Syria, such as oil refineries that enabled it to raise revenue by selling oil on the black market.