The Syrian province of Idlib is under relentless attack from the forces of Bashar al-Assad and his Russian and Iranian allies. There are more than three million people in the region, many of whom have already been displaced several times from elsewhere in Syria.

The enclave is subject to the Sochi agreement between Russia and Turkey, which was supposed to create a de-escalation zone to protect civilians from violence. However, in the past 12 months, Assad’s forces, backed by Russian aviation and mercenaries, as well as Iranian sectarian militias and Hezbollah, have launched a campaign against Idlib – it has been intensifying since December and is close to coming to a disastrous conclusion.

This week alone, we have seen airstrikes by Syrian and Russian forces on schools and nurseries in Idlib city, killing 21 people, amid further clashes. At least 33 Turkish soldiers, who back the opposition in the region, were also killed in airstrikes most probably carried out by Russia. As a result, more than a million people have been displaced towards the closed border with Turkey, more than 1,700 civilians – many of them children – have been killed in the bombardment and people are freezing to death in makeshift camps. All this under an indifferent gaze of the world and the powers capable of reining in Assad and his allies.

The main reason for such deadly inaction is the flawed understanding of the situation, whereby the slaughter of people in Idlib is seen as a tragic but unavoidable part of the Syrian endgame: if Russia and Assad conquer Idlib a certain number of innocents will die, goes this thinking, but the conflict will be over and the process towards reconstruction, the return of refugees and normalisation of Syria can start. A key element to this thinking is the fact that Hayat Tahrir al-Sham (HTS), a former al-Qaida affiliate, is in control of parts of Idlib and therefore Russians and Assad are given a free hand in “dealing with the terrorists”. The fact that three million people (who have consistently demonstrated against HTS’s rule) are going to be the collateral damage to this “anti-terrorist” slaughter draws nothing more than a shrug.

The consequences, however, are going to be catastrophic – and not only for Syrians. As is evident from the relentless and indiscriminate bombardment of Idlib, especially with inaccurate barrel bombs, summary executions of civilians and the barbaric desecration of graveyards, the people of Idlib are dehumanised in the eyes of those who attack them. If Idlib falls, we are likely to see large-scale executions of military-age men left in the region – under the accusation of terrorism or for rebelling against the government. This is a familiar tactic of Assad’s murderous regime.

A recent poll conducted on the ground by the Syrian Association for Citizens’ Dignity indicated that fewer than 10% of the people displaced by the Russian and Syrian onslaught would be willing to remain under Assad’s rule. This means vast numbers of people could leave, attempting to cross the closed border with Turkey. The country already hosts some four million Syrian refugees and says it cannot take any more. Most displaced Syrians are aiming to reach Europe, so Turkey may eventually facilitate that passage – in fact, this did start to happen after the deadly attack on its soldiers on Thursday. It is not hard to imagine the devastating impact another large-scale movement of refugees would have on European political dynamics.

Assad’s “victory” in Idlib (in reality a victory for Russia and Iran) would destroy any chance of a comprehensive and sustainable political solution to the conflict. It would prevent any significant return of refugees and people displaced in the country from taking part in future elections or reconstruction process. Russia and its puppet regime in Damascus will become more dismissive of concessions in the political process, with the international community losing any remaining credibility. A political solution under such conditions will be seen as an extension of the current Russian- and Iranian-backed regime: it will lack legitimacy in the eyes of the majority of Syrians and may lead to a new, deadly cycle of violent struggle.

These scenarios would be likely to prompt the US and EU to intensify sanctions targeting Assad and his sponsors, which would further destroy an already failed economy, with a devastating impact on the population. This would then see more movement of people towards Lebanon and Jordan. Meanwhile, any aid to rescue that population would end up in the hands of regime-controlled networks.

All this is just the tip of the iceberg. The worst and the most dangerous impact of a blatant dereliction of responsibility to the people of Idlib would be on its children and youth. What narratives would 1.5 million children of Idlib grow up on? If Idlib is allowed to fall, how could they ever be expected to buy into notions of justice, law and human rights? How would anyone be able to prevent them falling prey to the merchants of radicalism and nihilism? It is the Syrian youth who must be the engine of political, social and cultural change if Syria is ever to become a stable, peaceful country.

It is clear that the need for European and other powerful states to act on Idlib does not come from a moral imperative but from clear political and security interests. The immediate priority is to pressure Assad and Russia into a complete halt to all attacks on civilians and providing urgent aid to the displaced people. The west must not leave Turkey to be the sole force fighting to protect civilians in Idlib. Once the killing and the suffering of civilians is stopped, there must be a strong, concerted and unrelenting push to secure a meaningful political solution that will guarantee a safe environment for all Syrians. Firm economic pressure must be maintained to prevent any normalisation of the regime. Any reconstruction in Syria must be directly linked to a legitimate political solution. Syrians must not be made to choose between living under Assad’s regime and becoming perpetually displaced.

The humanitarian catastrophe that is Idlib has shown that the lessons from the second world war still apply: appeasement of dictators who are willing to kill massive numbers of people will never work. If Europe fails to heed those lessons again, it will not only be Syrians who pay the price.

• Labib al-Nahhas is the programme director of the Syrian Association for Citizens’ Dignity and a senior member of the Syrian political opposition