Outsiders can be forgiven for being tired of the Syrian conflict. After all, the violence has lasted for nearly a decade and the worst chapters – for outsiders, at least – have come and gone: Islamic State (Isis) seized almost half the country, in addition to one-third of Iraq and launched a global network of terror in 2014. But the world has now caught its breath and the threat has all but ended. Refugees, too, flooded Europe some years ago but the influx has been contained.

Also, expert warnings about a resurgence of violence or extremism did not materialise and the return of state control seems to be the steady trajectory of the conflict despite persistent problems. Most of the country is currently under the control of either the regime, Turkey or the United States-backed Kurdish forces in eastern Syria. Even in the Kurdish zone, many would concede that it might be just a matter of time before these areas are recaptured by Damascus, even without much fighting, if and when the US eventually ends its presence there.

Idlib has what it takes to sustain an underground insurgency against the regime

Still, the unravelling of the situation in the last area under rebel control merits renewed attention. Not only because the relentless campaign launched by the regime and its Russian and Iranian allies is causing one of the worst humanitarian disasters in recent memory – up to a million desperate people have been displaced. But also because the fallout, after the mass carnage, could shape events for a generation to come.

Idlib is distinct for two main reasons. One is related to the role it acquired during the Syrian conflict as it became a “dumping ground” for hardline fighters elsewhere in the country who refused to surrender to the regime. It now has many of the most committed opponents – not just fighters – to the dictatorship in Damascus. The second reason goes further back, as the areas around Idlib were once a staging ground for an insurgency against the father of the current president in the 1970s and 80s – it is no coincidence that it played a similar role after 2011.

Idlib has what it takes to sustain an underground insurgency against the regime, one that is likely to quickly spill over to pacified areas elsewhere in the country. In fact, Idlib could initiate a nationwide underground insurgency in ways that previous fights did not. It is well placed geographically and demographically. The area is adjacent to the heartlands of Bashar al-Assad’s regime in the coastal region and hosts the largest numbers of young individuals who bore arms during the conflict.

Also, northwestern Syria has become increasingly dominated by jihadist forces smarter than Isis in dealing with the communities in which they operate. They blended with the local communities and focused almost entirely on fighting the regime, rather than on seizing areas and “cleansing” them of those who might pose a future threat to them, as Isis did. This approach enabled these jihadists and their allies to build an infrastructure of local influence that could help them sustain a long-term insurgency, as they turn from governing to fighting.

The grievances that pushed Syrians across the country to rise up have not gone away, they have sharpened

Such violent forces are likely to inherit the legitimate cause of Syrians who rose against the dictatorship in Damascus to demand a dignified and better life. The grievances that pushed Syrians across the country to rise up have not gone away – they have sharpened. The regime’s killing and torture machine has destroyed countless families everywhere in Syria. Exhaustion, as previous conflicts such as the one in Iraq show, does not bring lasting peace. So jihadist forces will no doubt hold the flag of the anti-Assad cause longer and subsequently absorb the energy of those still committed to the cause.

The most significant objective achieved by Russia after its direct military intervention in 2015, which secured the regime, has been to pacify the rebel areas through de-escalation agreements brokered along with Turkey, once the most committed backer of the Syrian opposition. Russia divided the rebels by diverting the war effort to one area at a time, making it possible for the regime to recapture rebel areas, but the strategy did not resolve the underlying problems of the conflict and Idlib is where the diehard groups gather.

The shift to insurgency usually comes after the fight over territory is complete. So, once the rebels lose their last pocket in northwestern Syria, they are likely to launch an underground revolt and connect with existing and currently latent networks in eastern, central and southern Syria.

Such patterns have played out before. It took years for defeated insurgents in Iraq to regroup and rebuild and the most fanatical – Isis – inherited the landscape and filled the void. Insurgency is not an afterthought for jihadists; Syrian jihadists have long discussed the strategy as a future scenario, but until now they have had to prioritise the fight at hand.

The Russian approach, of recapturing areas, also does not resolve a lingering problem for the thinly stretched regime in Damascus, namely the lack of the manpower to fully control and police vast areas. In many cases, the regime’s “return” to areas previously controlled by the rebels amounts to little more than planting the Syrian flag in the town. A shift in the fighting from conventional means to underground revolt could see many of these areas falling back into rebel hands.

In short, outsiders should not judge the Syrian conflict solely on how the situation has played out in recent years as the regime and its international allies recaptured areas through vicious and relentless campaigns of terror. There is still one major chapter to come and one that could prove to be highly consequential.

• Hassan Hassan directs the non-state actors and geopolitics programme at the Center for Global Policy and is co-author of Isis: Inside the Army of Terror