ISIS (~Islamic State in Iraq and Syria) is an expansion of ISI (Islamic State in Iraq) and operates in both Iraq and Syria.
Until last year it was an al-Qaeda affiliate, now it may be an al-Qaeda rival.
The ISIS is a very radical Islamic organization whose stated objective is to use force and military conquest to reestablish the caliphate and to impose their idea of strict Islamic rule in the Middle East.
It uses an image of religious purity to raise large amounts of money from donors and to recruit many volunteers from around the world to 'fight for Islam'.
It is also a mafia-like organization which also raises a great deal of money through extortion, and looting, and selling what it has looted.
It is very disciplined, organized, and patient, and makes its plans very strategically.
It often uses those it recruits as cannon-fodder to protect its core of experienced fighters.
It is very mobile and will mount swift attacks on multiple locations which it considers to be the easiest available targets knowing that many will have to later be retreated from. The aim being to seize and hold whatever areas it can, to soften up and loot the areas that it can't hold, and to keep the forces which oppose it stretched thin over a large area.
It is ruthless in its administration of areas under its control, terrorizing those who live there. This makes these areas easier to control and has the added benefit for the ISIS of causing many who live in the areas which they control, and attack, to flee making these areas easier to control and to seize.
It makes alliances with other groups who delude themselves into believing that 'this time we can trust the ISIS' or 'after we take over this area together we can easily defeat the ISIS and take control of this area ourselves'. When the usefulness of those with whom the ISIS has allied itself ends, the ISIS will turn on and attack these former allies, justifying this by saying these groups aren't Islamic enough.
The ISIS Base in Syria
About two years ago radical Islamic insurrectionists (the announcement of the expansion of ISI to ISIS would come about a year later) began concentrating their operations and establishing their base in northeastern Syria, east of the Euphrates.
This area was lightly defended by Syrian government forces. The Euphrates formed a natural barrier. It borders western Iraq which is where the then ISI was based. It is the home of Arab tribes who have long historic ties to Kuwait, Qatar, and Saudi Arabia and these tribes provided very useful contacts and conduits for financing and supplies. It has borders with Turkey and Iraq across which supplies and fighters could be easily transported. And most of Syria's oil and gas resources are located in this area.
This area is also where most of the Syrian Kurds are located. The ISIS has tried, and still tries, to defeat the Syrian Kurds there to take advantage of the Turkish government's animosity towards the Syrian Kurds and also to try to take full control of most of Syria's oil and natural gas resources.
The Syrian Kurds, however, have been able to defeat the ISIS and to solidify their control over the two heavily Kurdish areas in Syria east of the Euphrates. The Syrian Kurds have also established control over three areas in northern Aleppo Governorate west of the Euphrates.
In the past year and a half as competition for supremacy among Syrian rebel groups grew, ISIS withdrew, and was sometimes forced to withdraw, almost completely to northeastern Syria, and at the same time ISIS forced most of its rebel rivals from this area.
This map fairly accurately indicates the current situation in this area:
This article is about ISIS's finances: