The CNN website provides this handy timeline of the development of the Islamic State.
2004 – Abu Musab al-Zarqawi establishes al Qaeda in Iraq (AQI).
2006 – Under al-Zarqawi, al Qaeda in Iraq tries to ignite a sectarian war against the majority Shia community.
June 7, 2006 – Al-Zarqawi is killed in a U.S. strike. Abu Ayyub al-Masri, also known as Abu Hamza al-Muhajer, takes his place as leader of AQI.
October 2006 – AQI leader Abu Ayyub al-Masri announces the creation of Islamic State of Iraq (ISI), and establishes Abu Omar al-Baghdadi as its leader.
April 2010 – Abu Bakr al-Baghdadi becomes leader of ISI after Abu Omar al-Baghdadi and Abu Ayyub al-Masri are killed in a joint U.S.-Iraqi operation.
April 2013 – ISI declares its absorption of an al Qaeda-backed militant group in Syria, Jabhat al-Nusra, also known as the al-Nusra Front. Al-Baghdadi says that his group will now be known as Islamic State in Iraq and the Levant (ISIS). Al-Nusra Front leader Abu Mohammed al-Jawlani rejects ISIS’s attempt to merge with the group.
February 3, 2014 – Al Qaeda renounces ties to ISIS after months of infighting between al-Nusra Front and ISIS.
May 2014 – ISIS kidnaps more than 140 Kurdish schoolboys in Syria, forcing them to take lessons in radical Islamic theology, according to London-based monitoring group Syrian Observatory for Human Rights.
June 9-10, 2014 – Monday night into Tuesday, militants seize Mosul’s airport, its TV stations and the governor’s office. ISIS frees up to 1,000 prisoners.
June 10-11, 2014 – ISIS takes control of Mosul and Tikrit.
June 20, 2014 – The United Nations announces that more than one million Iraqis have been displaced.
June 21, 2014 – ISIS takes control of Al-Qaim, a town on the border with Syria, as well as three other Iraqi towns.
June 28, 2014 – Iraqi Kurdistan restricts border crossings into the region for refugees.
June 29, 2014 – ISIS announces the creation of a caliphate (Islamic state) that erases all state borders, making al-Baghdadi the self-declared authority over the world’s estimated 1.5 billion Muslims. The group also announces a name change to the Islamic State (IS).
June 30, 2014 – The United Nations announces that an estimated 1.2 million Iraqis have been forced from their homes.
June 30, 2014 – The Pentagon announces the United States is sending an additional 300 troops to Iraq, bringing the total U.S. forces in Iraq to nearly 800. Troops and military advisers are sent to Iraq to support Iraqi security forces and help protect the U.S. Embassy and the airport in Baghdad.
July 2014 – ISIS takes control of Syria’s largest oilfield and seizes a gas field in the Homs Province, storming the facility and killing dozens of workers. Militants conquer a 90-mile stretch of Syrian towns, from Deir Ezzor to the Iraq border. In Mosul, they blow up Jonah’s tomb, a holy site dating back to the 8th century B.C.
August 6, 2014 – ISIS fighters attack the northern Iraqi town of Sinjar, home of a religious minority group called the Yazidis. A Yazidi lawmaker says that 500 men have been killed, 70 children have died of thirst and women are being sold into slavery. More than 30,000 families are stranded in the Sinjar Mountains.
August 8, 2014 – Two U.S. F/A-18 jet fighters bomb ISIS artillery units in Iraq. President Barack Obama has authorized “targeted airstrikes” if needed to protect U.S. personnel from fighters with ISIS. The U.S. military also could use airstrikes to prevent what officials warn could be a genocide of minority groups by the ISIS fighters.
August 19, 2014 – In a video posted on YouTube, U.S. journalist James Foley, missing in Syria since 2012, is decapitated by ISIS militants. The militants then threaten the life of another captured U.S. journalist, believed to be Steven Sotloff.
September 2, 2014 – ISIS releases a video showing the beheading of U.S. journalist Steven Sotloff. Sotloff’s apparent executioner speaks in the same British accent as the man who purportedly killed Foley.
September 11, 2014 – The CIA announces that the number of people fighting for ISIS may be more than three times the previous estimates.
September 13, 2014 – ISIS militants post video on a website associated with the group, showing the apparent execution of British aid worker David Haines. This makes him the third Western captive to be killed by the Islamist extremist group in a single month. At the end of the video, another British captive, Alan Henning, is shown and apparently threatened.
September 23, 2014 – The United States carries out airstrikes against ISIS.
October 3, 2014 – ISIS releases a video showing the apparent beheading of hostage Alan Henning. In the same video, the group threatens the life of American aid worker Peter Kassig, also known as Abdul-Rahman Kassig.
November 3, 2014 – The Iraqi government announces ISIS militants have killed 322 members of the Albu Minr tribe in a recent series of executions.
November 14, 2014 – The U.N. Independent International Commission of Inquiry on Syria concludes that ISIS has committed war crimes and crimes against humanity.
November 16, 2014 – ISIS militants claim to have beheaded American hostage Peter Kassig in a video published to the Internet. Peter Kassig, also known as Abdul-Rahman Kassig, is the fifth Westerner whom ISIS claims to have beheaded via video messages.
January 17, 2015 – According to an Iraqi Kurdistan official, ISIS has released about 250 Yazidis. Many are children and the elderly.
January 20, 2015 – ISIS demands $200 million from Japan in exchange for the lives of two Japanese hostages, Kenji Goto and Haruna Yukawa.
January 22, 2015 – U.S. diplomatic officials say that coalition airstrikes have killed an estimated 6,000 ISIS fighters to date, including half of the top command of the terror group. U.S. intelligence officials estimate that ISIS still has 9,000 to 18,000 fighters and thousands of sympathizers.
January 24, 2015 – An ISIS supporter posts an online video of hostage Kenji Goto, holding a photo of beheaded hostage Haruna Yukawa. The video includes a demand for the release of terror suspect Sajida al-Rishawi, from Jordan, in exchange for Kenji Goto.
January 31, 2015 – ISIS releases a video online showing the decapitated body of journalist Kenji Goto.
February 3, 2015 – Video and still images posted online by ISIS supporters apparently show Jordanian military pilot Moath al-Kasasbeh being burned alive while confined in a cage.
February 5, 2015 – Jordanian fighter jets carry out airstrikes over Syria, reportedly hitting ISIS training centers and arms and ammunition depots in ISIS’s de facto capital, Raqqa.
February 6, 2015 – In an online post, ISIS claims that Jordanian airstrikes killed American hostage Kayla Jean Mueller. The post contains a picture of a collapsed building, which ISIS claims Mueller was buried beneath. There is no proof of her death.
February 10, 2015 – Kayla Jean Mueller’s family announces she is dead, after receiving confirmation from ISIS, including a photo of her wrapped in a burial shroud.
February 11, 2015 – U.S. President Barack Obama asks Congress to formally authorize use of military force against ISIS.
February 15, 2015 – In an ISIS video, militants appear to behead 21 Egyptian Christians on a Libyan beach. On February 16, Egyptian warplanes stage airstrikes against ISIS targets in Libya in retaliation.
February 20, 2015 – Three simultaneous suicide car bomb blasts kill at least 30 and injure more than 40 in Gobba, Libya. Wilayat al-Barqa, the Libyan branch of ISIS, claims responsibility for the explosions.
February 22, 2015 – ISIS releases a video that appears to show at least 21 Kurdish Peshmerga fighters in cages paraded down Iraqi streets. The last scene of the video shows them alive.
February 26, 2015 – Jihadi John, the disguised man with a British accent who appears in ISIS videos as the executioner of Western hostages, is identified as Mohammed Emwazi, a Kuwaiti-born Londoner. On the same day, ISIS releases a video of its fighters destroying antiquities at the Mosul Museum.
March 1, 2015 – ISIS releases 19 Christian prisoners from a group of 220 Assyrians captured in northern Syria.
March 4, 2015 – ISIS releases images of a man being thrown off a building in Raqqa, Syria. This is one in at least half a dozen cases in which ISIS has killed a man for allegedly being homosexual.
March 7, 2015 – In an audio message purportedly from Boko Haram leader Abubakar Shekau, the Nigeria-based radical Islamic group pledges allegiance to ISIS.
March 12, 2015 – In an audio message, a speaker identified as an ISIS spokesman claims the caliphate has expanded to western Africa and that ISIS leader Abu Bakr al-Baghdadi has accepted Boko Haram’s pledge of allegiance. On the same day, Iraqi forces retake most of Tikrit from ISIS, and ISIS blows up the Iraqi army headquarters north of Ramadi, killing at least 40 Iraqi soldiers.
April 8, 2015 – According to Iraqi Kurdistan officials, ISIS releases more than 200 Yazidi women and children, as well as the ill or elderly.
April 19, 2015 – The terror network’s media arm releases a video of ISIS operatives beheading two groups of prisoners, including 30 Ethiopian citizens, at different locations in Libya.
May 16, 2015 – A U.S. Special Operations raid in Syria results in the killing of a key ISIS figure and the capture of his wife. U.S. officials say the raid yields significant intelligence on ISIS’s structure and communications.
May 17, 2015 – ISIS seizes control of Ramadi, the largest city in western Iraq, after government security forces pull out of a military base.
May 21, 2015 – ISIS takes control of Palmyra, a 2,000-year old city in the Syrian desert. According to the Syrian Observatory for Human Rights, it was the last Syria-Iraq border crossing under control of Syrian troops.
June 1, 2015 – During a speech, Gen. Hawk Carlisle describes how the U.S. military uses social media as a tool to track militants. Carlisle says that an ISIS member posted a “selfie” on social media, revealing a command post. Within 22 hours, the U.S. military was able to identify the target and perform airstrikes, destroying the compound.
June 14, 2015 – A British teen, Talha Asmal, is reportedly one of four ISIS suicide bombers who attack the headquarters of a Shia militia group in Iraq, killing at least 11. Before the bombing, ISIS posted photos of Asmal, 17, posing next to their black flag on social media. According to the BBC, Asmal left England in March to join the Islamic fundamentalists.
June 19, 2015 – The State Department issues its annual terrorism report, declaring that ISIS is becoming a greater threat than al Qaeda. The frequency and savagery of ISIS attacks are alarming, according to the report.
June 24, 2015 – The Syrian government reports that ISIS militants have destroyed two Muslim holy sites in Palmyra. The group attacked a 500-year-old shrine and a tomb where a descendent of the Prophet Mohammed’s cousin was reportedly buried.
June 26, 2015 – A gunman kills at least 38 people at a beachfront Tunisian hotel, and a bomb kills at least 27 people at a mosque in Kuwait. ISIS claims responsibility for the attacks.
July 1, 2015 – ISIS launches simultaneous attacks on five Egyptian military checkpoints, reportedly killing 17 Egyptian soldiers and injuring 30 others. According to the Egyptian military, 100 terrorists are killed in the fighting.
July 4, 2015 – The Syrian Observatory for Human Rights reports it has received a video showing ISIS militants executing 25 captives in the Syrian city of Palmyra.
July 17, 2015 – As Iraqi civilians celebrate Eid al-Fitr, a holiday marking the end of the fast for Ramadan, ISIS detonates an ice truck in a crowded marketplace in Khan Bani Saad, killing at least 120 people and wounding at least 160 more.
July 2015 – According to IHS Jane’s, the territory controlled by ISIS saw a 9.4% reduction in the first six months of 2015, and is now approximately 32,000 square miles.
August 2015 – ISIS destroys antiquities in the historic city of Palmyra in Syria, including the nearly 2,000-year-old Temple of Baalshami. UNESCO, the U.N.’s cultural organization, calls the destruction of the temple a “war crime.”
November 12, 2015 – The Pentagon announces that a remote control drone strike targeting Islamist militant Mohammed Emwazi, also known as “Jihadi John,” struck a vehicle that Emwazi was seen getting into. The strike took place in Raqqa, Syria, the defacto ISIS capital. ISIS later confirms the death of “Jihadi John.”
November 12, 2015 – Two suicide bombs hit the Bourj al-Barajneh district of southern Beirut, killing over 40 people and wounding hundreds. ISIS claims responsibility for the attack stating that the attackers had arrived in Lebanon from Syria two days before.
November 13, 2015 – After a two-day battle, the Peshmerga Iraqi Kurdish military force declares victory in liberating the Iraqi town of Sinjar from ISIS. The battle was backed by the U.S. coalition air power.
November 13, 2015 – Three teams of gun-wielding ISIS suicide bombers hit six locations around Paris, killing at least 129 people and wounding hundreds.
December 10, 2015 – A spokesman for the U.S.-led coalition comfirms that ISIS Finance Minister Abu Saleh was killed in an airstrike in late November in Iraq.
December 28, 2015 – Iraqi troops retake the city of Ramadi from ISIS and raise the Iraqi flag on top of the government compound in the city’s center, according to an Iraqi military spokesman.
January 24, 2016 – ISIS releases a video that purports to show final messages from the Paris attackers.
February 21, 2016 – Multiple attacks in Homs and southern Damascus kill at least 122 and injure scores, according to Syria’s state-run SANA news agency. ISIS claims responsibility for the attacks.
 “ISIS Fast Facts” CNN (27 Feb 2016). http://edition.cnn.com/2014/08/08/world/isis-fast-facts/.