With the evacuation of the last of its armed rebels and their families, last month, the Syrian city of Aleppo is once again in the hands of the Assad government. Aleppo had a prewar population of more than two million people; it was not only Syria’s largest city and its industrial powerhouse but had an iconic place as one of the world’s oldest continuously inhabited cities, with a history dating back some eight thousand years. Before the war, Aleppo’s wealth of ancient buildings and its cosmopolitan mix of sects and peoples—Sunni Arabs, Shiites, Kurds, Turkmen, Alawites, Circassians, Chechens, Greeks, Assyrian and Armenian Christians, and even a few Jews—made it a matchless place in the modern Middle East. It remains to be seen what, of all that, has survived.

The fighting and destruction will go on elsewhere in Syria. The combined Syrian-government-Russian-Iranian military offensive that crushed resistance in Aleppo after months of sustained bombardment will undoubtedly soon move southwest to the province of Idlib, bordering Turkey, where most of Aleppo’s evacuees have congregated. The ISIS “caliphate” of Raqqa has yet to be reconquered, along with numerous smaller Syrian towns and cities. But Aleppo’s fall is a momentous milestone, and probably marks the beginning of the end for Syria’s myriad rebel factions, five and a half years after their uprising began.

When a loose coalition of rebels invaded Aleppo’s eastern suburbs, in July, 2012, I joined one of the factions at a schoolhouse, which the rebels had turned into a forward base. It was a disquieting experience. Instead of an atmosphere of heady triumph, I found the air rife with fear and suspicion. In one of the classrooms, a couple of dozen cowed-looking men were being held prisoner; when I asked about them, a taciturn fighter shooed me away. A little while later, a commotion erupted when several rebel fighters surrounded one of their comrades and accused him of being a spy. As they grabbed at him, he screamed furiously and tried, unsuccessfully, to get away. He was overpowered and hustled down a corridor by the men; I didn’t learn his fate.

In an attempt to approach the city’s ancient citadel, which was still held by government forces, a companion and I clambered into a car with a handful of gunmen and drove deeper into the city. From the hard stares we received from civilians we passed on the street, it seemed clear that not all of Aleppo’s residents were pleased about their “liberation” by the rebels, and as we approached the city center, gunshots rang out. Feeling ourselves to be in a dangerous no-man’s land, we turned back.

A few days after we left Aleppo, we learned that the same rebels who had hosted us had executed a group of four men they accused of betrayal. The rebels made a cell-phone video of the execution, in which several fighters fired hundreds of bullets at the four men, who had been lined up against a schoolyard wall, during a forty-five-second spree. The wall was painted with large pictures of cartoon characters, including Mickey Mouse and SpongeBob SquarePants.

Another day, in a rebel-held town situated a couple of hours to the north of Aleppo, I attended the funeral of a young man detained and killed by regime security agents; his body, which had been recovered by his family, showed a number of puncture wounds, but there were also several large gouges, where chunks of flesh were missing. One of his relatives wondered if this had had been done with pliers, as part of his torture, while he was still alive.

Four and a half years later, the results of Aleppo’s cruel standoff have been devastating. Large swaths of the once great city lie in ruins, with incalculable damage done to its historic and archeological monuments. Sections of the citadel, the minaret of the city’s storied Umayyad Mosque, and large sections of its medieval souk have either been destroyed or sustained heavy damage. Some of the city’s physical patrimony may yet be restored, but the remarkable blend of peoples that once made Aleppo such an exceptional place seems likely to have been lost forever.

The conflict has taken an unbearably high toll in human life. As many as half a million people have been killed in Syria since the unrest began, in 2011, including untold thousands in Aleppo alone. Life expectancy for Syrians has dropped by an average of twenty years, and infant mortality has increased by ten per cent; poverty and malnutrition are rife throughout the country. An estimated twelve million people, or nearly half of Syria’s prewar population of twenty-three million people, have been displaced, including nearly five million who have fled the country altogether to crowd into refugee camps in Turkey, Jordan, Lebanon, Iraq, and Egypt, where they are dependent on international humanitarian assistance for their survival. Another million Syrians have smuggled themselves into Europe, where many live uncertain lives in holding centers as they await decisions on asylum petitions.

Few conflicts in the modern era have been as bleakly apocalyptic or as globally destabilizing as Syria’s, and its consequences will be felt widely for decades to come. Those who have survived its horrors firsthand will have to bear the trauma of personal losses that include the deaths of loved ones and physical injuries; the pain and humiliation of torture, including sex slavery and gang rape; the loss of homes and property; the effects of prolonged shock and fear caused by incessant aerial bombardment; starvation; imprisonment; flight and exile; and so on.

Far beyond Syria, as well, many millions of people bear indelible memories of the conflict’s multifarious savageries, thanks to the numbing barrage of videos that have been posted on Facebook and Twitter and YouTube. These include the mass executions of prisoners by bullet and sword, by fire and drowning; the final moments of hapless, terrified individuals being thrown off buildings and being stoned to death; young children converted into merciless executioners; and a thousand other prurient horrors. Many of us live with the harrowing memory of the journalist Jim Foley’s face, or of Steven Sotloff’s, in the moments before a hooded tormentor sawed their heads off, and we will never be the same for it.

How difficult it is now to reconjure up the widespread public optimism of the spring of 2011, when Syria was engulfed in the passionate upheaval proclaimed to be an “Arab Spring,” an upwelling of democratic fervor sweeping through the Middle East, a seemingly unstoppable and overwhelmingly positive force. So much has changed since then. Egypt’s heady Tahrir Square “revolution” degenerated into public gang rapes and President Hosni Mubarak’s substitution by a cultish new military dictatorship; Libya’s revolt led to Muammar Qaddafi’s gruesome murder on YouTube, and left behind a ruined country; ISIS extended its reach from Syria’s hydra-headed civil war to reignite Iraq’s sectarian conflict and launch a global terror campaign that is ongoing.

The Western leaders who once aided and abetted the Arab Spring as a vehicle for democratic change in the Middle East—Nicolas Sarkozy and David Cameron come to mind—are either gone from the political stage or, like Barack Obama, are making their final exit. The reputations of each of these men were, in different ways, tarnished by the decisions they took with regards to the Middle East during their time in power. Obama stepped back from the brink of military intervention after the Syrian regime’s use of chemical weapons against civilians, in 2013, and is now being succeeded in the White House by Donald Trump.