Islamic State of Iraq and the Levant/Founder -
Abu Musab al-Zarqawi
https://en.wikipedia.org/wiki/Abu_Musab_al-Zarqawi
Convinced the Americans would invade Iraq, Zarqawi began building a base there in 2002; when they did so a year later, he proved willing to ally with remnants of Saddam’s intelligence network. The story is well told by William McCants in his excellent new book, The ISIS Apocalypse. Four months after the U.S. invasion, Zarqawi’s organization attacked three well-chosen targets—UN headquarters in Baghdad, the Jordanian embassy in Baghdad, and the Imam Ali Mosque, a Shiite shrine, in Najaf—that signaled the dirty war ahead. These bombs shattered the ground for reconciliation: Iraq would be a no-go zone for the international organizations that might have lightened the burden of U.S. occupation; Iraq’s links would be severed with its mainstream Sunni patron, Jordan; and Iraq would be cleaved apart by a vicious sectarian war between Sunni and Shiite Muslims, whose coexistence had been a feature of modern Iraqi life. Zarqawi’s game plan was set by late August 2003; at the time, the United States was still denying there was an insurgency in the country.
....
A few embers of Zarqawi’s Islamic state remained, kept alive by flickering Sunni rage. The flame was nurtured at U.S.-organized Iraqi prisons such as Camp Bucca, where religious Sunni detainees mingled with former members of Saddam’s Baath Party, and the nucleus of a reborn movement took shape.
...
It helped too that ISIS had used Iraqi prisons as its training camps, building trust, operations security, and a passionate hatred for the Shiite-led government in Baghdad. This was a guerrilla army in waiting, and ISIS staged a campaign called “Breaking the Walls” to free these captives and bring them into the fight. Whiteside estimates that between July 2012 and July 2013, ISIS orchestrated seven major prisons raids, culminating in a spectacular, well-organized breakout at Abu Ghraib. (One of the first things ISIS did after sweeping through Mosul was to liberate the prison there, adding several thousand fighters to its burgeoning ranks.) One graduate of these prisons turned schools for jihad, Abu Bakr al-Baghdadi, is the current leader of ISIS.
http://www.theatlantic.com/international/archive/2015/10/how-isis-started-syria-iraq/412042/
According to a 2015 study by the Financial Action Task Force, ISIL's five primary sources of revenue are as followed (listed in order of significance):
proceeds from the occupation of territory (including control of banks, oil and gas reservoirs, taxation, extortion, and robbery of economic assets)
kidnapping for ransom
material support provided by foreign fighters
fundraising through modern communication networks
In 2014 the RAND Corporation analyzed ISIL’s funding sources by studying 200 documents — personal letters, expense reports and membership rosters — captured from the Islamic State of Iraq (which included al-Qaeda in Iraq) by US Forces in Iraq between 2005 and 2010.[3] It found that over this period, outside donations amounted to only 5% of the group’s operating budgets, with the rest being raised within Iraq. In the time period studied, cells were required to send up to 20% of the income generated from kidnapping, extortion rackets and other activities to the next level of the group's leadership. Higher-ranking commanders would then redistribute the funds to provincial or local cells which were in difficulties or which needed money to conduct attacks. The records show that the Islamic State of Iraq depended on members from Mosul for cash, which the leadership used to provide additional funds to struggling militants in Diyala, Salahuddin and Baghdad.
In mid-2014, Iraqi intelligence obtained information from an ISIL operative which revealed that the organisation had assets worth US$2 billion, making it the richest jihadist group in the world. About three-quarters of this sum is said to be represented by assets seized after the group captured Mosul in June 2014; this includes possibly up to US$429 million looted from Mosul’s central bank, along with additional millions and a large quantity of gold bullion stolen from a number of other banks in Mosul. However, doubt was later cast on whether ISIL was able to retrieve anywhere near that sum from the central bank, and even on whether the bank robberies had actually occurred.
https://en.wikipedia.org/wiki/Finances_of_ISIL
Islamic extremist fighters captured U.S.-made Humvees and tanks from a crumbling Iraqi Army.
ISIS captured large swathes of territory in northern Iraq. The Iraqi Army, trained by the U.S., collapsed in the face of ISIS advances due to poor training, broken equipment and low morale. They left behind arms, munitions and equipment that were produced and paid for by the United States, which has given $25 billion to train and arm the Iraqi Army and other branches of security forces since 2003, the year the U.S. invaded Iraq. So now ISIS possesses hundreds of Humvees, pickup trucks, tanks and armored vehicles, as well as ammunition and artillery shells. They have used those weapons to continue to march through Iraq and to help out their fight in neighboring Syria, where ISIS is battling the government of Bashar al-Assad.
http://www.alternet.org/world/how-isis-ended-stocked-american-weapons
It took advantage of ex-Iraqi officers' experience
ISIS fighters got better, in part because they were being led by former officers of Saddam's army. The United States disbanded Iraq's army in 2003 to start a new one from scratch, leaving many Sunni officers out of work. Remember the Sunni resentment against the new Shiite-led government? Some aggrieved Sunni officers joined the insurgency, and eventually ISIS.
It skillfully used prison 'networking'
By now, many of its top leaders were former inmates at US-administered prisons in Iraq during the insurgency. Those prisons, it appears, were networking centers for those who would join the movement. Analysts say Baghdadi and some of his top deputies were at various points imprisoned at Camp Bucca, which was a US-run prison in southern Iraq.
http://edition.cnn.com/2016/08/12/middleeast/here-is-how-isis-began/
Now tell me why they did so?
As the self-proclaimed worldwide caliphate, their mission is to establish Islam as the supreme form of government for all Muslims throughout the world. This means implementing all Islamic traditions as they were initially laid out by Muhammad and forcibly expanding their territory.
The current leader is Abu Bakr al-Baghdadi. His lineage, as a descendant of Muhammad's tribe, the Quraysh, supposedly gives him authority to act as a legitimate caliph (leader of the caliphate).
https://www.quora.com/How-did-ISIS-form-When-and-where-did-ISIS-begin
Started to see the truth yet?
The truth is murky, multi-faceted and fluid.
