Islamic State of Iraq and the Levant

Islamic State of Iraq and the Levant (ISIL), or Islamic State of Iraq and Syria (ISIS), or Islamic State, (IS) is a Wahhabi jihadist militant and terrorist group. In Arabic it is often called "Daesh". It operates in Libya, Nigeria, Syria and a small part of northern Iraq. It is influenced by the Wahhabi Sect of Islam. It claims the status of independent state for the territories under its control in Iraq, Libya, Nigeria, and Syria. It is opposed to Shiism and has been described as "Shiaphobic".
The group was started in the early years of the Iraq War and associated itself with Al-Qaeda in 2004. ISIL was composed of different insurgent groups. Its aim was to establish a caliphate in the Sunni majority regions of Iraq, later expanding this to include Syria. In February 2014, after an eight-month power struggle, Al-Qaeda cut all ties with ISIL.
ISIL is millenarianist, meaning it believes that society is going to change a lot, and everything we know will end soon. The group recruits new members by promising them sex slaves or cheap marriages.
Fighting
At the height of the Iraq War, ISIL was in the Iraqi provinces of Al Anbar, Ninawa, Kirkuk, most of Salah ad Din, parts of Babil, Diyala and Baghdad. It claimed Baqubah as its capital. In the ongoing Syrian Civil War, the group has a large presence in the Syrian governorates of Ar-Raqqa, Idlib and Aleppo.
The group has attacked government and military targets. It has claimed responsibility for attacks that killed thousands of Iraqi civilians. During the time coalition forces were present in Iraq, the group suffered some setbacks. By 2012, it was thought to have regained most of its strength and more than doubled the number of its members to about 2,500.
In 2013, a letter and an audio recording of Ayman al-Zawahiri, the leader of al-Qaeda, was leaked to Al Jazeera. In it, al-Zawahiri disbanded the Syrian faction of ISIL. The group's leader, Abu Bakr al-Baghdadi, opposed this ruling on the basis of Islamic law. The group has since continued to operate in Syria. Starting in April 2013, it made rapid military gains in large parts of Northern Syria, where the Syrian Observatory for Human Rights described them as "the strongest group". They have sought publicity by releasing videos of the decapitation (beheading) of journalists and other prisoners of war mainly done by member Jihadi John. He was killed in November 2015.
Worldwide Caliphate
In June 2014, it announced a worldwide caliphate. In 2014, ISIL successfully fought in a large-scale offensive in Iraq. After this offensive, ISIL is reported to have seized control of most of Mosul, the second biggest city in Iraq, its surrounding Nineveh province, and the city of Fallujah. In the spring of 2015 ISIL fought for control of Tikrit, the administrative center of the Salah ad Din Governorate.
In spring of 2016 the Army of Iraq took back Fallujah. At the end of 2016 the army took back Ramadi in Al Anbar Province, and in early 2017 Iraqi government forces retook Mosul. In October, Raqqa, the former headquarters, fell.
Film
The 2014 film The Blue Man, which is related to The New York Times article titled "Uncovering Iraq's Horrors in Desert Graves" written by John F. Burns, also mentions mass killings of Shia Muslims by the Islamic State between 2003 to 2006.
References
Caliphates
Iraq
Shiaphobia
Syria