(CNN)Here's a look at Islamic State in Iraq and Syria (ISIS).
Started as an al Qaeda splinter group.
ISIS is known for killing dozens of people at a time and carrying out public executions, crucifixions and other acts. It has taken over large swaths of northern and western Iraq.
The group currently controls hundreds of square miles. It ignores international borders and has a presence from Syria's Mediterranean coast to south of Baghdad. It rules by Sharia law.
Dabiq, Syria "is where the Prophet Mohammed is supposed to have predicted that the armies of Islam and 'Rome' would meet for the final battle that will precede the end of time and the triumph of true Islam," according to CNN National Security Analyst Peter Bergen.
ISIS's strategy for revenue includes oil production and smuggling, ransoms from kidnappings, selling stolen artifacts, extortion and controlling crops.
Abu Bakr al-Baghdadi: Very little is known about al-Baghdadi, but a biography posted on jihadist websites in 2013 said he earned a doctorate in Islamic studies from a university in Baghdad.
He formed the militant group in Salaheddin and Diyala provinces north of the Iraqi capital before joining al Qaeda in Iraq.
Al-Baghdadi was detained for four years in Camp Bucca, which was a U.S.-run prison in southern Iraq. He was released in 2009.
After ISIS declared the creation of the so-called "Islamic State," he began using the name Al-Khalifah Ibrahim, and now goes by that name with his followers.
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 in 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 8, 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).
April 2013 - 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.
June 9, 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, 2014 - ISIS takes control of Mosul.
June 11, 2014 - ISIS takes control of Tikrit.
June 28, 2014 - Iraqi Kurdistan restricts border crossings into the region for refugees fleeing the fighting.
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 sent to Iraq are there to add security to the U.S. Embassy and the airport in Baghdad, and to provide support to Iraqi security forces.
July 2014 - In Syria, all the cities between Deir Ezzor city and the Iraq border have fallen to ISIS, says Omar Abu Leila, a spokesman for the rebel Free Syrian Army.
July 17, 2014 - In Syria's Homs province, ISIS claims to have killed 270 people after storming and seizing the Shaer gas field.
August 8, 2014 - Two U.S. F/A-18 jet fighters bomb artillery of Sunni Islamic extremists 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 what sounds like the same British accent as the man who purportedly killed Foley. He's dressed identically in both videos, head to toe in black, with a face mask and combat boots. He appears to be of similar build and height. He waves a knife in his left hand, as did the militant in the video of Foley's death.
September 11, 2014 - The CIA announces that the number of people fighting for ISIS may be more than three times the previous estimates. Analysts and U.S. officials initially estimated there were as many as 10,000 fighters, but now ISIS can "muster between 20,000 and 31,500 fighters across Iraq and Syria," a CIA spokesman tells CNN.
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 recent weeks. ISIS directs a statement at British Prime Minister David Cameron, threatening more destruction if Britain continues its "evil alliance with America." At the end of the video, the executioner threatens the life of Alan Henning, another British citizen held captive. The executioner appears to be the same one who killed both Steven Sotloff and James Foley.
October 3, 2014 - ISIS releases a video showing the apparent beheading of hostage Alan Henning. It blames the killing on the UK for joining the U.S.-led bombing campaign against ISIS in Iraq and Syria. 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. According to Sheikh Nabil Al-Ga'oud, a leader in the Albu Minr tribe, the latest of these incidents occurred November 1, in which 75 members of the tribe were killed near the town of Hit.
November 13, 2014 - An ISIS social media account posts an audio message purportedly recorded by leader Abu Bakr al-Baghdadi. The speaker is heard saying the U.S.-led coalition to destroy ISIS is "terrified, weak and powerless." The 17-minute audio says the coalition's effort has been a "failure" and the coalition will be "forced" to "send ground forces to their deaths and destruction." The speaker also urges Islamic State fighters to take their battle everywhere and "light the Earth with fire upon all tyrants," and mentions U.S. President Barack Obama's plan to deploy 1,500 additional U.S. troops to Iraq "under the claim they are advisers." CNN cannot confirm the authenticity of the online message or when it was recorded.
November 14, 2014 - The U.N. Independent International Commission of Inquiry on Syria concludes that ISIS has committed war crimes and crimes against humanity, and leaders of the militant group should be held accountable by organizations such as the International Criminal Court.
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. The masked executioner, referred to as Jihadi John, states,"We bury the first crusader in Dabiq, eagerly waiting for the rest of your armies to arrive."
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 thousands of ISIS fighters to date, including half of the top command of the terror group. The number may be as high as 6,000 or higher, according to U.S. ambassador to Iraq Stuart Jones.
January 24, 2015 - Posted online is a video of hostage Kenji Goto, holding a photo of beheaded hostage Haruna Yukawa. A voice in the video demands 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. Jordanian state TV says that al-Kaseasbeh was killed on January 3.
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. Foreign Minister Nasser Judeh claims the airstrikes are just the beginning of Jordan's retaliation over the murder of Moath al-Kasasbeh.
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. Jordanian Interior Minister Hussein Majali calls the online post a "PR stunt." The Pentagon estimates ISIS has about 20,000 to 30,000 fighters.
February 15, 2015 - In a new propaganda video released by ISIS, the group appears to behead 21 Egyptian Christians on a Libyan beach. On February 16th, 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 new propaganda video, which appears to show at least 21 Kurdish Peshmerga fighters in cages paraded down Iraqi streets. The last scene of the video shows them alive, but a man threatens, "We say to the Peshmerga: Leave your jobs or your fate will be like these, either the cage or under the ground."
February 26, 2015 - "Jihadi John," the disguised man with a British accent who appears in ISIS videos as the executioner of Western hostages, has been 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 - Without explanation, ISIS releases 19 Christian prisoners from a group of 220 Assyrians captured the week prior 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 5, 2015 - Iraq's Ministry of Tourism and Antiquities announces that ISIS has razed the ancient city of Nimrud by bulldozing the site.
March 12, 2015 - In an audio message, a speaker purportedly identified ISIS spokesman Abu Mohammed al Adnani, claims the caliphate has expanded to western Africa and that ISIS leader Abu Bakr al-Baghdadi has accepted Boko Haram's the pledge of allegiance. On the same day, ISIS blows up the Iraqi army headquarters north of Ramadi, killing at least 40 Iraqi soldiers.