IS (Islamic State, or ad-Dawla al-Islamiya) is an armed extremist Islamist umbrella group which originated in Iraq as Jama'at al-Tawhid wal-Jihad in 1999, led by the Jordanian salafist Abu Musab al-Zarqawi. JTJ participated in the insurgency in the wake of the 2003 invasion of Iraq by Western forces at the behest of the United States and pledged allegiance to al-Qaeda in October 2004. On 7 June 2006, a US airstrike killed al-Zarqawi, who was succeeded by the Egyptian militant Abu Ayyub al-Masri. In October 2006 JTJ in coalition with a number of other jihadi groups and Sunni tribes, declared the establishment of the Islamic State of Iraq (ISI), comprising Iraq's six mostly Sunni Arab governorates. Following the deaths of al-Masri ISI came under the leadership of Abu Bakr al-Baghdadi, and the group began its transformation into IS, which culminated in the declaration of the caliphate in June 2014.

Al-Baghdadi reinforced ISI:s strongholds in Iraq's Anbar and Nineveh provinces and recruited a number of high ranked officers from Saddam Hussein's former army. On 8 April 2013, al-Baghdadi claimed that the jihadist militia al-Nusra front in Syrias civil war had been established by ISI and proclaimed an Islamic State in Iraq and the Levant (ISIL); in arabic: ad-Dawla al-Islamiya fi Iraq wa sh-Sham (ISIS). This claim was refuted by al-Nusra front's leader Abu Mohammad al-Julani and the leader of al-Qaida, Ayman al-Zawahiri. al-Qaida would eventually withdraw their support for ISIL.

A coalition of rebel forces including The Free Syrian Army pushed ISIL out of Aleppo in January 2014, but ISIL continued to recruit members in Syria and steadily gained ground in Iraq. In Iraq, ISIL was able to capture most of Fallujah in January 2014, and in June 2014 was able to seize control of Mosul. On 29 June 2014 ISIL proclaimed itself to be a worldwide caliphate, and thereby claiming religious, political and military authority over all Muslims worldwide. Abu Bakr al-Baghdadi was named its caliph, and the group renamed itself ad-Dawlah al-Islāmiyah, the Islamic State (IS).

In the wake of a collapsing Iraqi army and a Syria in turmoil IS quickly advanced in Iraq and Syria. During 2015 the territory claimed by the group reached from Fallujah in the South, Mosul in the northeast, Manbij close to the turkish border in Northern Syria and Palmyra in the Syrian desert. The group installed a strict and harsh version of Sharia law in their territories and gained a worldwide notoriety for their brutality.

From 2015 IS started to gain followers worldwide, not the least because of their internet campaigns. A number of jihadi groups, such as Boko Haram in Nigeria, swore formal allegiance to IS. In early February 2015, IS militants in Libya managed to capture part of the countryside to the west of Sabha, and later, an area encompassing the cities of Sirte, Nofolia, and a military base to the south of both cities, and established a presence in Yemen, Afghanistan and other countries.

The group claimed responsibility for a string of high-profile terrorist attacks outside Iraq and Syria from 2015. These, often well organized, attacks targeted civilians and police and included shootings, mosque bombings, downing of airplanes and attacks with unsophisticated weapons such as knives or transport vehicles. IS was also involved in mass killings, even at times with a genocidal intent such as in the case of the Yazidi population in the Sinjar mountain.

Eventually IS opponents forced the group to retreat from their strongholds. Russia entered the war on the side of Syria's dictator Assad in September 2015. A coalition headed by USA and UK supported opposition groups and rebel factions and trained the Kurdish Peshmerga forces that efficiently defended the Kurdish areas in Northern Syria and Northeastern Iraq. The French, the Iranians and the Saudis sent troops and air support. The Turks in coalition with rebels intervened from the north.

On July 10, 2017, Iraqi Prime Minister Abadi formally declared a local Iraqi victory over IS after the Iraqi army expulsion of the group from the city of Mosul after a fierce battle. On 17 October 2017, IS lost control of Raqqa. On 3 November, Deir ez-Zor, the groups last major city in Syria, was recaptured, as well as Rawa, the last town held by IS in Iraq. IS was also defeated in Libya in November 2017. By the end of November most of IS territory in Iraq and Syria had been recaptured. Even though the group still has a presence in several countries around the world, and keep mounting terrorist attacks, the era of the caliphate in Iraq and Syria have seemingly been brought to a halt.

This article has been compiled from the following sources:

Uppsala Conflict Data Program (Date of retrieval: 2018-08-05) UCDP Conflict Encyclopedia, Uppsala University. http://ucdp.uu.se/#actor/234
Wikipedia Islamic_State_of_Iraq_and_the_Levant, published under the GNU FDL. Retrieved 2018-08-05
Wikipedia Islamic_State_of_Iraq, published under the GNU FDL. Retrieved 2018-08-05
Wikipedia International_military_intervention_against_ISIL, published under the GNU FDL. Retrieved 2018-08-05