For the past three years, ISIL has tried to establish a footing in southern Syria. It tried in the mountainous Qalamoun region near the Lebanese border, but it was expelled after intermittent clashes with Al Qaeda and Hizbollah. Its attempts to co-opt forces near Damascus did not get far either, particularly as rebels preemptively clamped down on the group’s fledgling cells there.

Following its failure to grow organically, it opted last year for a pincer strategy to link up its pockets of control between Palmyra and Homs to ones in Damascus’s north east, such as Dumayr. That effort also failed since its territory in the Homs desert was largely cleared by the pro-government forces in April. The group was also expelled from the Palestinian Yarmouk camp after a brief takeover in April last year.

But there is now bad news. In Deraa, ISIL may see not only an opening but that the opening could be the first of its kind in the whole of Syria since the group was formed in April 2013.

Last month, three local groups in Deraa formed Jaysh Khaled bin Al Walid. ISIL announced the merger on Friday. The groups -- namely the Yarmouk Martyrs Brigade (YMB), Islamic Muthanna Movement (IMM) and Mujahideen Group – operate mainly in western Deraa. Last Thursday, the US state department designated the YMB as a terrorist group.

For ISIL, the south in general is strategically and symbolically important. Deraa borders Israel and Jordan and has historical resonance. The new formation is named after the historical Muslim figure, Khaled bin Al Walid, who commanded a key battle in the Yarmouk Basin against the Byzantine empire in the 7th century.

Nowhere in Syria has ISIL succeeded in growing organically as it has done in Deraa. This is a remarkable development especially since the Southern Front has been hailed as a good example of international support to the opposition.

Members of the three factions are overwhelmingly locals from Deraa. Many of them are part of prominent tribes in the province. Members often describe the movement as more extreme than Jabhat Al Nusra. Unlike other areas in Syria, these groups have become loyal to ISIL voluntarily rather than because they had no other choice.

The name change to Jaysh, or army, is also meant to affirm the subordination of these groups to ISIL since the organisation does not recognise “movements” or “groups”. The word “Jaysh” suggests the new group will operate as other ISIL’s military sections, such as Jaysh Al Khilafah or Jaysh Al Badia. Restructuring of the merged groups is already underway, with reports that the new leader, Abu Othman Al Shami from Idlib, arrived shortly before the merger took place.

ISIL will probably seek to alter the way the new force operates. Before they unified, the three forces were in a constant conflict against rebel forces in Deraa but they rarely coordinated. Recently, the groups started to collaborate but they were also weakened as factions inside the province pushed back against them with help from the multi-country Military Operations Centre in Amman.

The new group will undoubtedly have different priorities and might seek to protect its forces, especially after the US and other countries, including Russia, appear to be turning more attention to it in that region. ISIL is not about to throw such hard-earned strategic assets into an open battle. A combined strategy of persistent fighting and quiet outreach will be its focus, a familiar move by the group.

ISIL will probably benefit from two main factors to increase its presence in Deraa. The Southern Front, a coalition of nationalist forces operating in the south, has been bitterly criticised by people in Syria because it has not conducted meaningful military operations against the regime in recent months. Military stagnation in that region, while Aleppo and Daraya were pounded, is seen as a result of foreign backers’ tight control of the Southern Front – unlike the situation in the north where Turkey provides unfettered support to its allies.

Another factor that might help ISIL is that one of the factions of Jabhat Al Nusra, which was known to have strong knowledge of ISIL’s operatives and cells in Deraa, had relocated to northern Syria. Unlike other anti-government forces, aside from ISIL, Jabhat Al Nusra has an effective underground apparatus that regularly uncovered ISIL cells undetected by the rebels, whether in Idlib, Homs, Deraa or eastern Syria. Examples are abundant, including the YMB.The loyalty of three groups in the Yarmouk Basin to ISIL presents more than a military challenge. Their members are combat ready and locally entrenched in a strategic area in which ISIL long desired to build influence. These groups are still outnumbered and can be defeated, but the story of how ISIL could establish presence despite persistent setbacks sheds light on its long game.

Hassan Hassan is a resident fellow at the Tahrir Institute for Middle East Policy and co-author of ISIS: Inside the Army of Terror

On Twitter: @hxhassan