°®Âþµº

The Islamic State group's war machine is driven by oil, and geared to finding new "slaves" and war booty, according to a recent disclosure of some of the organisation's secret files.

Documents captured by US special forces, and revealed by Reuters on Monday, appear to show an organisation dogged by antiquated command structures, including a department for "war spoils".

Although the department has likely been busy given IS' year-and-a-half expansion in Iraq and Syria, the group also appears riddled with petty squabbles and internal rivalries that could dog its success.

IS' rapid takeover of eastern Syria and northern Iraq in June 2014 was seen by many military analysts as a revolutionary campaign by a non-state actor.

The extremist group continued its territorial expansion in 2014, but in recent months IS has conceded ground to Kurdish-Syrian rebel forces and the Iraqi army.

Experts believe that the documents seized during a US special forces raid in May - which killed IS finance chief Abu Sayyaf - will give US officials a better understanding of the workings of the group and how best to tackle it.

One thing noted was the organisation appears burdened by its pursuit for "statehood".

This has created an organisation that is bureaucratically heavy with multiple committees and departments running its territories.

Its oil industry - seen as the lifeline of the group - is also riddled with a "meticulous and data-orientated" command structure, which makes its operations look "unsophisticated", one energy expert told Reuters.

Perhaps the most antiquated wing of the group is the department managing "war spoils", which includes "slaves".

The files seized from captured hard drives, USBs, CDs and documents list a series of documents to ensure the subjugation of people in its territories.

This details a bewildering number of macabre, disturbing and mundane rulings on everything from the "permission" for fighters to rape women, the treatment of "slaves", and when theft is allowed.

With such a convoluted system, it is unsurprising that the IS command structure appears riddled with rivalries.

This was evident in one letter from one IS' department placing Abu Sayyef in charge of stolen antiquities:

"The reason being is that he is very knowledgeable in this field and that Abu Jihad al-Tunisi is a simpleton who can't manage the division."