Damascus was designated a state sponsor of terrorism in 1979, and it has lived up to that title every year since. Syria’s descent into civil war presented several opportunities to dispense with the despot in Damascus and avert a crisis in the process, but they were all ignored. As I wrote for National Review, Syria is a case study in the perils of ideological non-interventionism. The results of the West’s over-reliance on covert action, outsourcing, and diplomacy in Syria is arguably the worst-case scenario.

Had Barack Obama not abandoned his infamous “red line” in 2013, the U.S. might have preserved the 100-year prohibition on the battlefield use of chemical weapons. The collapse of that taboo has been rapid and terrifying. In the years that followed, chemical arms have been regularly deployed in Syria, and rogue powers have been using complex nerve agents on foreign (even allied) soil in reckless state-sponsored assassination campaigns.

Ideological adherence to non-interventionism well after it had proven an untenable course of action allowed the flourishing of terrorist organizations. Some parties in the West with a political interest in isolationism deliberately confused these terrorist groups with secularist movements led by Assad regime defectors. In the years that followed, those moderate rebel factions were crushed or corrupted while Islamist terror networks, which provided a politically valuable contrast to the “civilized” regime in Damascus, were patronized and nurtured by Assad.

The incubation of terrorist organizations eventually necessitated the kind of American military intervention Obama had so desperately sought to avoid, but at a time and place not of America’s choosing and with a footprint too small to achieve any permanent solution to the crisis. All the while, a great human tide poured out from Syria in all directions, but especially into Europe. There, an influx of unassimilated migrants eroded the continent’s post-War political consensus and catalyzed the rise of illiberal populist factions.

Even as late as the summer of 2015, there was still time for the West to summon the courage to do what was necessary. In a stunning speech that summer, Assad himself admitted that Syrian forces suffered from “a lack of human resources” amid Western estimates that nearly half the 300,000-strong Syrian army had been killed, captured, or deserted. “Based on current trend lines, it is time to start thinking about a post-Assad Syria,” an intelligence source told the Washington Post’s David Ignatius. But Obama dithered still. Just a few short weeks later, Vladimir Putin, upon whom Obama relied to help him weasel out of his pledge to punish Assad for his crimes, intervened in Syria on Damascus’s behalf. That was when the greatest crimes began.

Russian intervention in Syria began not with attacks on “terrorists,” as Moscow claimed, but with attacks on covert CIA installations and arms depots; a dangerous campaign that continued well into the Trump era. The Syrian regime and its Iranian and Russian allies then embarked on a scorched-earth campaign. They bombed civilian neighborhoods and hospitals and maternity wards. They surrounded the liberated cities of Homs and Aleppo, barraging and starving their people into submission. They even targeted and destroyed a United Nations aid convey before it could relieve the famine imposed by Damascus. All the while, Moscow’s propagandists mocked reports of these atrocities, and the children who stumbled bloodied and ashen from the ruins of their homes were deemed crisis actors by Russian officials and their Western mouthpieces.

America’s strategic obligations in Syria did not diminish with Russian intervention. They increased, but so too did the danger. Early on, Russian forces concentrated not just on attacking Assad’s Western-backed enemies but on harassing NATO-aligned forces that were already operating in the Syrian theater. Russian warplanes harassed U.S. drones, painted allied assets with radar, conducted near-miss fly-bys of U.S. warships and airplanes in the region, and repeatedly violated Turkish airspace. This conduct was so reckless that, in November of 2015, NATO-allied Turkish anti-aircraft fire downed a Russian jet. On the ground, Moscow and Washington engaged in the kind of proxy fighting unseen since the collapse of the Soviet Union, as U.S.-manufactured armaments were routinely featured in rebel-made films of successful attacks on Russian tanks and APCs.

In the years that followed this intensely dangerous period, the Syrian state did not recover. Instead, Syrian forces withdrew to a narrow area along the coast and around the capital and left behind a vacuum that has been filled by competing great powers. Iran, Russia, Turkey, Jordan, Saudi Arabia, Qatar, the United Arab Emirates, Canada, the United Kingdom, France, Australia, and the United States, to say nothing of their proxy forces, are all competing to control and pacify portions of the country. Even if the terrorist threat is one day permanently neutralized in Syria—a prospect that today seems far off, considering these nations’ conflicting definition of what constitutes a terrorist—the state of competition among these powers ensures that the occupation of Syrian territory will continue for the foreseeable future.

And now, the final battle is upon the rebels. On Friday, hundreds of Syrians waving the “independence flag” poured into the streets of Idlib, the last of the country’s free cities, begging the international community to spare them from the onslaught that has already begun. The United Nations has warned that up to 800,000 people could be displaced in Damascus’s efforts to retake the rebel-held enclave, and the worst of the seven-year war’s humanitarian disasters may be yet to come.

Over the last two weeks, the United States has issued some ominous warnings. Senior American officials have begun telling reporters that the evidence is increasing of Damascus’s moving chemical munitions near the frontlines with the intent of using them on civilians. Trump administration officials announced in no uncertain terms that they would respond to another chemical attack with disproportionate force.

In response to these threats, Moscow deployed the biggest Russian naval taskforce on the Syrian coast since 2015. Simultaneously, Russia has warned of its intent to strike “militant” positions in the country’s Southwest, where U.S. soldiers routinely patrol. American forces are holding firm, for now, and the Pentagon insists that uniformed personnel are at liberty to defend themselves if they come under assault. If there is a conflict, it wouldn’t be the first time Americans and Russians have engaged in combat in Syria.

In February, Russian mercenaries and Syrian soldiers reinforcing columns of T-72 tanks and APCs armed with 125-millimeter guns engaged a position just east of the Euphrates River held by American Green Berets and Marines. The four-hour battle that ensued resulted in hundreds of Russian fatalities, but it may only have been a terrible sign of things to come.

Of course, a Western-led intervention in the Syrian conflict would have been accompanied by its own set of setbacks. What’s more, the political backlash and dysfunction that would have accompanied another difficult occupation in the Middle East perhaps presented policymakers with insurmountable obstacles. But the course the West followed instead has been a disaster.

The lessons of the Syrian civil war are clear: The U.S. cannot stay out of destabilizing conflicts in strategically valuable parts of the world, no matter how hard it tries. The humanitarian and political disasters that resulted from Western indifference to the Syrian plight is a grotesque crime that posterity will look upon with contempt. Finally, the failure to enforce prohibitions against chemical-weapons use on the battlefield has emboldened those who would use them recklessly. American soldiers will suffer the most in a world in which chemical warfare is the status quo of the battlefield of the future.

American interventionists are often asked by their opponents to reckon with the bloodshed and geopolitical instability their policies encourage. If only non-interventionists would do the same.