the inside story of isis: The dramatic rise of isis, capturing large territory, having strong & professional army, oil rich land, How isis is managing to administrate such a large territory.

In 2011 following the outbreak of demonstrations in Ramadi, a series of demonstrations happened all over Iraq to demand the resignation of the Iraqi prime minister. Instead of dialogue, the Iraqi govt started to repress and crackdown the Sunni demonstrators, and this led the country to an all-out civil war.
During one of these demonstrations, a black flag was raised among the demonstrators, and soon this flag became the rally flag for the Sunnis who were promised vengeance from the government for the cruel killings of Sunni Muslims during the crackdown.
With the support of middle-class, Sunni families and the backing of Sunni tribesmen, a group under the name of ISLAMIC STATE OF IRAQ started their first operation to wipe out the Iraqi army from the Sunni-dominated province of Anbar under the code name of ANBAR CAMPAIGN. The cities and towns fell with such shocking speed that even some of the leaders of the group were surprised by their victories.
Soon they expanded their territory to Syria by taking an active part in the Syrian civil war and grabbed the oil rich land of Syria. With the capture of a large territory in Syria, the group renamed itself the ISLAMIC STATE OF IRAQ AND SYRIA or simply ISIS or ISIL.
After the shocking rise of ISIS, the international community was afraid of the expansion of this group to Eastern Europe, the Gulf States, and South Asia. So a coalition of 14 countries led by the United States of America started air strikes against ISIS targets, mainly in Iraq, rarely in Syria. However, due to guerilla warfare and lack of intelligence reports from the ground, the ISIS group initially resisted the threat well. They even succeeded in expanding their territory further.
In September 2015, following a formal request from Syria, Russia started its own aerial campaign against ISIS in Syria, the commitment of the Russian president to defeat ISIS was praised throughout the world. Russia started intensive airstrikes against the ISIS positions in Syria and unlike the US-led coalition, these air strikes proved effective in allowing the Syrian army to gain ground and halt the advances of the rebels and ISIS fighters.
However, the resilience of ISIS was stunning, and the new wave of air strikes was insufficient to break the operational momentum of the Isis fighters and its main administrative framework.
Unlike hundreds of other terrorist and insurgent groups, ISIS has maintained a unique administrative structure; they announced their ministries for different services such as civil services, war ministry, finance ministry, oil ministry, information ministry, cyber ministry, etc. This was followed by a new structure of the bureaucracy. ISIS is taking taxes from the civilians and provides them with enough services to enable them to keep in contact with the civilian population and separate from other terrorist organizations.
Unlike other insurgent groups which mainly consist of emotionally motivated fighters, the ISIS army consists of professional fighters They collect funds and sell oil from the oil fields under their control so that they can pay their fighters and they pay them well. An average fighter of Isis gets $200-400 per month.
Some of the Sunni Muslim states such as Turkey, KSA and UAE are backing them due to their own interests in Iraq and Syria. The Iranian and Saudi blocks are fighting proxies in Syria, Yemen, and Iraq.
In Iraq and Syria, the Saudi block is helping ISIS and rebels. Iran is backing the governments of these countries, but in Yemen the situation is inverted: there the Saudi block is backing the govt while the Iranian block is helping Houthi rebels to fight against the govt.