President Obama authorised targeted air strikes against the Islamic State's positions to stop its fighters from advancing further towards the Iraqi Kurdish region and to help avert an act of genocide against a religious minority the group considers devil-worshippers, the Yezidis.

The move, uncharacteristic of intervention-averse Obama, highlights how the jihadist group has expanded and become an unstoppable force, six months after it seemed it would not even complete a year in existence, when major rebel factions in Syria declared war against it earlier this year.

The group, which became known as the Islamic State of Iraq and Syria (Isis) after it broke away from the al-Qaida-affiliated Jabhat al-Nusra in April last year, had been driven out of most of Syria, and rebel factions and al-Qaida affiliates threatened to chase it out of Iraq. But the group has made a remarkable comeback, seizing stretches of at least seven provinces in the two countries, and marching steadily into other areas.

In the last two weeks alone, Isis has fought on five fronts: against the Iraqi army, the Kurdish peshmerga, the Syrian regime, the Syrian opposition and the Lebanese army. In Syria the group has all but consolidated control of the eastern provinces of Raqqa and Deir Ezzor, as it made advances against government forces in Raqqa and subdued most of the rebel forces in Deir Ezzor. It is also advancing into Aleppo, reaching the city's eastern outskirts, and in Hasaka, and is battling the Kurdish militias in the north-east. In Iraq it has advanced to a point only half an hour's drive from Irbil, the Kurdish capital.

Yet these advances appear to be only the tip of the iceberg. Away from the publicised gains, Isis is quietly making progress on other fronts. Perhaps the most worrying is the fact that armed groups backed by the US have been co-opted by Isis.

After its sweeping military success in Iraq in June, Isis moved to take over the strategic province in Deir Ezzor, where the rebels controlled lucrative oil and gas resources. To the surprise of many, the group quickly controlled towns and villages that were home to some of the group's most powerful adversaries, including Jabhat al-Nusra and locally rooted tribal militias.

According to Samer al-Ani, an opposition media activist from Deir Ezzor, several fighting groups affiliated to the western-backed Military Council worked discreetly with Isis, even before the group's latest offensive. Liwa al-Ansar and Liwa Jund al-Aziz, he said, pledged allegiance to Isis in secret, with reports that Isis is using them to put down a revolt by the Sha'itat tribe near the Iraqi border.

He warned that money being sent through members of the National Coalition to rebels in Deir Ezzor risks going to Isis. Another source from Deir Ezzor said that these groups pledged loyalty to Isis four months ago, so this was not forced as a result of Isis's latest push, as happened elsewhere. Such collaboration was key to the takeover of Deir Ezzor in recent weeks, especially in areas where Isis could not defeat the local forces so easily.

This is not the first, or the only, time in which groups affiliated to the military structures backed by the US and the Gulf states have worked with Isis. Saddam al-Jamal, a top commander for the Free Syrian Army's eastern front, pledged allegiance to Isis in November and fought in its ranks, wreaking a grisly carnage in his hometown of Abu Kamal in April. Other groups affiliated to the western-backed military councils that have pledged allegiance to Isis include Liwa Fajr al-Islam in Homs.

Moderate religious groups that had been established mostly to fight jihadists are now working closely, if quietly, with Isis. Liwa Ahl al-Athar, for example, has discreetly pledged allegiance to Isis. The Salafi-leaning rebel alliance, which has a strong presence in many areas in Deir Ezzor and beyond, is financially backed by private donors from the Arab Gulf states, but is said to be in the "good guys" list by governments that back the Syrian opposition.

A provincial leader of the alliance in Abu Kamal, according to an influential opposition figure in the area, is related to an Iraqi emir of Isis and has worked with the jihadist group to mediate a truce with the Sha'itat tribe. According to the same source, other rebel groups have often travelled to the Iraqi border town of Husaiba to win support from Isis for leadership in their areas.

Moreover, Isis has followed new strategies during its latest offensive, in Iraq and Syria, to establish long-term presence in the areas it controls. Such strategies include greater leeway for local forces to run their daily state of affairs, instead of the old strategy of directly managing these areas. In areas where it still fears an uprising, the group maintains direct control. Isis is also planning to recruit foreign jihadists within the ranks of groups co-opted by it to ensure their loyalty.

Even in Deraa, where Jabhat al-Nusra has steadily consolidated its presence, sources say that Isis has supporters close to the top leadership of the al-Qaida affiliate and there are clans willing to declare allegiance to Isis. Increasingly, Isis is becoming more sophisticated and resilient. Contrary to speculations that the group is overreaching itself, Isis gains the loyalty of more forces every time it controls a new area. It is expected that if the group makes headway into Aleppo, members of like-minded jihadi factions such as Ahrar al-Sham will defect and join its ranks.

Beyond its advertised victories, Isis is building a vast network of supporters even within moderate ranks that could help it persist in the face of a military action similar to this weekend's American air strikes.

Time appears to be on its side, and unless there is a comprehensive political and military approach to fight it in both Iraq and Syria the group is here to stay.

Hassan Hassan is an analyst at the Delma Institute, a research centre in Abu Dhabi, and a columnist for the National newspaper. Follow him on Twitter @hxhassan