The Islamic State (IS), also known as the Islamic State of Iraq and the Levant (ISIL; ˈaɪsᵻl), Islamic State of Iraq and Syria (ISIS; ˈaɪsᵻs), and by its Arabic acronym Da'ish or Daesh (داعش, Dāʿish, ˈdaːʕɪʃ), is a transnational militant Islamist terrorist group and former unrecognized quasi-state that follows the Salafi jihadist branch of Sunni Islam.
It was founded by Abu Musab al-Zarqawi in 1999 and gained global prominence in 2014, when it captured a large amount of Iraqi territory, and took advantage of the civil war in Syria to take control of chunks of territory in Eastern Syria. By the end of 2015, it held an area estimated to contain eight to twelve million people stretching from western Iraq to eastern Syria, where it enforced its interpretation of Islamic law, administered an annual budget of more than billion and had more than 30,000 fighters under its command. By 2019 it had lost the last of its Middle Eastern territories and returned to insurgency in the regions it once controlled, operating from remote hideouts, and continuing its propaganda efforts.
From 2003 to 2013, the group pledged allegiance to al-Qaeda (mostly under the name "Islamic State of Iraq") and participated in the Iraqi insurgency against the United States and its allies. The group changed its name again to "Islamic State of Iraq and Levant" for about a year, before proclaiming itself to be a worldwide caliphate, called simply the Islamic State (الدولة الإسلامية, ad-Dawlah al-Islāmiyah). As a caliphate, it demanded the religious, political, and military obedience of Muslims worldwide, despite the rejection of its legitimacy by mainstream Muslims and its statehood by the United Nations and various governments.
For the next few years the Iraqi Armed Forces and the Syrian Democratic Forces beat back "the Islamic State" and degraded its financial and military infrastructure, assisted by advisors, weapons, training, supplies and airstrikes by the U.S.