“We're going to see a massacre on a scale that has never been seen during this entire war.” These are the words of UN deputy regional humanitarian coordinator for Syria, Mark Cutts, speaking to Sky News about the Assad regime’s ongoing Russian and Iranian-backed slaughter of Idlib.

For years the entirety of the international community has had exhaustive and irrefutable proof that Syria’s dictatorship has been carrying out a campaign of human extermination against its civilian population, with a death toll in the hundreds of thousands. There is indisputable evidence that the regime has been responsible for using chemical weapons and deliberately targeting hospitals, UN aid convoys, paramedics, schools, civilian homes and civilian infrastructure.

This regime has used starvation, torture, rape and displacement as weapons of war. How much worse can it get? Idlib is home to three million Syrians, one million of them children, with the overwhelming majority of the population already displaced from other parts of the country. How did those people end up in Idlib?

While Western leaders were insisting there was no military solution to the conflict in Syria, Russian President Vladimir Putin’s military intervention to save the crumbling Assad regime proved that was a lie. Moscow’s sponsorship of Assad has allowed him to pursue a campaign of mass aerial bombardment of civilian infrastructure, while the international community’s response has been to issue strongly worded statements about ceasefires.

After nearly a decade of civil war, Syria’s opposition is broken and fragmented. Having received no significant international support, most of Syria’s democratic military opposition groups have been disbanded or devoured by hardline Islamists. The regime, which has never made a distinction between civilian, democratic, armed or Islamist opposition, has used their presence to justify the bombing of hospitals with impunity.

After each rebel-held city in Assad’s sights had been besieged and starved, the UN would help the regime bus this broken and forcibly displaced civilian population off to Idlib. Former residents of rebel-held areas that do not flee are routinely rounded up and sent to the same death camps that pro-democracy activists never returned from in the early days of the Syrian revolution – a process of systematic, human extermination and depopulation.

The UN stopped counting the death toll in Syria more than four years ago, with a UN envoy estimating it stood at more than 400,000 people. That number did not include the hundreds of thousands of missing Syrians kidnapped by the government for taking part in anti-regime demonstrations. With the near-daily bombardment Syrians have faced for the last four years, how much of an underestimate do you think that number is? The true horror of the Syrian civil war is now beyond human comprehension. We will never know how much blood has been spilt, and by achieving their final military solution in Syria, Assad and Putin will make sure nobody will ever be able to answer that question.

There is nowhere left to turn for Idlib’s three million people. The Syrian Civil Defence has documented more than 2,000 airstrikes and 600 barrel bombs during the regime’s offensive. Nine hundred thousand people have been forced to flee and entire cities of tents line Idlib’s border with Turkey. The Assad regime is now bombing those too.

Turkish president Recep Erdoğan, an ally of Russia and Iran, but an opponent of Assad, briefly prevented the Russian and regime offensive by setting up military observation posts in Idlib and promising Russia it would curb the growing influence of extremist groups in the area such as Hayat Tahrir al-Sham. Turkey’s main interest in Syria remains preventing the establishment of a separatist Kurdish state, and its appalling human rights record, including the crimes of militias it has recruited to fight Kurdish groups, should put into perspective how little hope anyone should have for Idlib.

So, how much worse the situation could become is not the question we should be asking. The question we should be asking is how many more human beings have to die before the world responds to the knowledge that it already has – that what is happening in Syria is the deliberate, systematic and calculated extermination of a civilian population.

There are no good options left, the opportunity for the world to prevent the slaughter in Syria passed the moment it refused to act when the regime started bombing its own cities. But while the international community kept fooling itself that it could freeze the conflict, the regime and Russia maintained their relentless blitzkrieg until only Idlib was left.

Ankara’s temporary agreement with Moscow over Idlib has now collapsed, and Turkey and the lives of three million human beings are now all that stands between the regime and its goal to burn every inch of Syria left outside of Assad’s rule.

We are now at the precipice, standing aside as Assad’s wanton slaughter makes a mockery of the lie we told ourselves after the fall of Nazi Germany. We built post-war international institutions and human rights law on the basis that we would never let this happen again. Yet every single time we ask that question again, we fail.

Syrians cannot afford this failure. The only options left on the table are a total regime military conquest, or the establishment of a military deterrent to protect civilians, and that is a political choice that needs to be made now to prevent the imminent massacre. The world decided long ago that hundreds of thousands of dead Syrians didn’t matter, so why should millions?

Ankara is now under immense pressure to halt the Syrian offensive, but if the international community does not unite to finally protect Syrians in Idlib, nothing will stop this regime from butchering every last man, woman and child standing in its way.

We know what the end game is in Syria, the blood has been shed for nine years and the smoke from Assad’s crematoriums will blacken and choke the skies of the Levant for at least another decade.

Every second we spend not acting to prevent this is an act of complicity.