BEIRUT—For at least a year before the summer of 2016, civilians and fighters in rebel-held East Aleppo prepared for a siege they believed was both avoidable and inevitable. Correctly, it turns out, they calculated that the opposition’s bankrollers and arms suppliers—the United States, Turkey, Saudi Arabia, and other “friends of Syria”—cared little for the well-being of civilians in rebel-held areas. Through the spring, contacts inside Aleppo prepared for the siege, expending minimal effort on appeals to the international community, which they assumed would be futile.

For all the world-weary resignation of the opposition fighters and other residents of rebel Aleppo, they have a well-earned pride in what they’ve done. They’ve maintained their hold on half of the jewel of Syria, and under withering assault, have cobbled together an alternative to Bashar al-Assad’s rule. “From the beginning of the revolution, we held Aleppo as the role model of the liberated city, that holds free elections, has an elected city council, and elected local committees that truly represent the people,” Osama Taljo, a member of the rebel city council in East Aleppo, explained over the phone after the siege began in earnest. “We insisted to make out of Aleppo an exemplar of the free Syria that we aspire to.”

Unfortunately, Aleppo has become an exemplar of something else: Western indifference to human suffering and, perhaps more surprisingly, fecklessness in the face of a swelling strategic threat that transcends one catastrophic war.

The last few weeks have piled humiliation upon misfortune for Aleppo, one of the world’s great cities, and already a longtime hostage of Syria’s never-ending conflict. Aided by the Russian military and foreign sectarian mercenaries, Syrian forces encircled East Aleppo over the summer. Rebels briefly broke the siege, but Assad’s forces fully isolated them just as Russia and the United States put the finishing touches on a dead-on-arrival ceasefire agreement that, contrary to its stated purpose, ushered in one of the war’s most violent phases yet. Instead of a cessation of hostilities, Syria witnessed an acceleration of the war against civilians, with East Aleppo as the showcase of the worst war-criminal tactics Assad has refined through more than five years of war.

Sieges violate international law, as well as specific United Nations resolutions, that, on paper, guarantee access to humanitarian aid to all Syrians but which in practice the government has disregarded. Aleppo—the biggest prize yet for Assad—has also been subjected to his most destructive assault. Throughout East Aleppo, Syrian or Russian aircraft have ruthlessly bombed civilians, singling out all healthcare facilities and first-responder bases. Bombs have ravaged well-known hospitals supported by international aid groups, along with the facilities of the White Helmets, the civil defense volunteers famous for digging casualties from rubble.

As if to test the proposition that the international community has just as little concern for its own reputation as it does for the lives of Syrian civilians—nearly half of whom have been displaced from their homes nationwide—Russia apparently chose, on September 19, the seventh day of the ceasefire, to bomb the first aid convoy en route to rebel-held Aleppo. That decision will be remembered as a fateful one.

Russia and Syria were following a timeworn blueprint: Use force to kill and starve civilians, then lie brazenly to avoid responsibility. In this case, the evidence is too clear and the trespass too toxic to let pass. So far, we’ve seen a sharp turn in rhetoric from the UN and Washington. Sooner or later, whether in the twilight of the Obama administration or in the dawn of his successor’s, we will see a much harder “reset” in Western relations with Russia.

For years, voices from Syria have raised the alarm. After years of dithering, even some members of the international community had the decency to follow suit, like Zeid Ra’ad Al Hussein, UN High Commissioner for Human Rights. “The country is already a gigantic, devastated graveyard,” al Hussein said this summer, warning Syria’s belligerents that sieges and intentional starvation campaigns amount to war crimes. “Even if they have become so brutalized [that] they do not care about the innocent women, children, and men whose lives are in their hands, they should bear in mind that one day there will be a reckoning for all these crimes.”

Belatedly, Western leaders are joining the chorus. UN Secretary General Ban Ki Moon, who avoided taking a stand during years of violence against humanitarian organizations by the Assad regime, now publicly accuses Syria and Russia of war crimes. On September 30, the one-year anniversary of Russia’s direct entry into the war, Gareth Bayley, Britain’s Special Representative to Syria, issued a broadside. “From Russia’s first airstrikes in Syria, it has hit civilian areas and increasingly used indiscriminate weapons, including cluster and incendiary munitions. Its campaign has dramatically increased violence and prolonged the suffering of hundreds of thousands of civilians,” he said, blaming Russia for at least 2,700 civilian deaths. “Russia has proved to be either unwilling or unable to influence Assad and must bear its responsibility for the Assad regime’s atrocities.”

America’s top diplomats, too, rail against Russia futilely. In a recently leaked recording of a meeting between a ham-handed but apparently sincere U.S. Secretary of State John Kerry and members of the Syrian opposition, Kerry admitted that he lost the internal debate in the administration for greater intervention, more protection of civilians, and a stiffer stand against Russia’s triumphalist expansionism. But like a good soldier, he has continued to flog a bad policy, pushing perhaps much too hard on the small constituency of opposition Syrians who remain committed to a pluralistic, unified, democratic Syria.

Perhaps Russia has been searching for the West’s actual red lines all along, exploring how far it could go in Syria without provoking any push back from the United States and its allies. Maybe it finally found them after it bombed the UN aid convoy in September. Only time will tell if the recent pitched rhetoric translates into action.

One of the few consistent goals of U.S. policy in Syria over the last year was to shift the burden of responsibility for the crisis, or even guilt, to Russia. Throughout long negotiations, Washington has bent over backwards to act in good faith, trusting against all evidence that Russia was willing to act in concert to push Syria toward a political settlement. America’s leaders today appear shocked that Russia was acting as a spoiler, a fact clear to most observers long ago.

With the latest agreement in ashes—literally—and an ebullient Russia convinced it will encounter no blowback for its war crimes, America has a political chit in its hands. For now, Russia thinks it can achieve its strategic goals by relentlessly destabilizing the international order and lying as gleefully and willfully as the Assad regime. The United States helped underwrite that international order when the UN came into being in 1945, laying down moral markers on atrocities like genocide and war crimes, and crafting a web of interlocking institutions that increased global security and prosperity. As its primary enforcer, the United States also has been its primary beneficiary.

Now that Russia, determined to reestablish its status after the humiliating collapse of the Soviet Union, has pushed the United States into a humiliating corner and weakened that international order, it is raising the stakes. Either the United States will push back, or the disequilibrium will spread even further. In either case, many thousands more Syrians will perish. As Bassam Hajji Mustafa, a spokesman for the Nour al-Din al-Zinki Movement, one of the more effective, if violent, rebel militias influential around Aleppo, put it, “People have adapted to death, so scaring them with this siege is not going to work.” Those who remain in Aleppo echo this refrain again and again: The last holdouts have stayed out of conviction. It’s hard to imagine anything but death driving them out. “If Aleppo falls and the world stays silent, then that will be the end of the revolution,” Hajji Mustafa said.

In the end, Aleppo is not a story about the West; it is a cornerstone of Syria and an engine of wealth and culture for the entire Levant. Aleppo is the story of the willful destruction of a pivotal Arab state, a center of gravity in a tumultuous region in sore need of anchors. It’s a story of entirely avoidable human misery: the murder of babies, the destruction of homes, the dismantling of a powerful industrial and craft economy.

The institutions of global governance are under strain and international comity is frayed; as yet, however, none of the steps toward dissolution are irreversible. Such shifts take place over decades, not months. But the crisis in Syria presents the most acute test yet, and demands of the United States an active, robust, and strategic response that reinforces its commitment to the architecture of global governance—a system threatened by spoiler powers like Russia and ideological attacks from nativists, the right-wing fringe, and other domestic extremists in the West.

Ignoring its responsibilities in Syria—and opening the door for Russia to pound away at the foundations of the international order—hurts not only Syrians but the entire world. Perhaps, finally, Assad and his backers have gone far enough to provoke an American defense of that indispensable order that America helped construct.