"The Islamic State (IS, aka the Islamic State of Iraq and the Levant, ISIL/ISIS, or the Arabic acronym Da'esh) is a transnational Sunni Islamist insurgent and terrorist group that controlled large areas of Iraq and Syria from 2014 through 2017. The group attracted a network of global supporters and its leader, Abu Bakr al Baghdadi, received pledges of affiliation from groups in several other countries. A series of terrorist attacks attributed to the group or to individuals it has inspired have claimed hundreds of lives on four continents since November 2015, including in the United States. While U.S. and allied forces in 2017 and 2018 successfully liberated most of the territory formerly held by the group in Syria and Iraq, IS leadership remains at large and IS fighters appear to be evolving into an insurgent force. The group's international affiliates continue to operate, and individuals inspired by the group continue to attempt attacks in Europe and elsewhere."
CRS Report for Congress, R43612
Congressional Research Service: https://crsreports.congress.gov/