This was not strictly true: HTS had been biding its time in its stronghold of Idlib province, on Syria’s northwestern border with Turkey, for five years since a ceasefire brokered by Turkish and Russian negotiators in 2020, avoiding direct confrontation with the regime and building its own structure outside state control.

Its parallel government included several ministries and a civil administration, the Syrian Salvation Government, governing a population of four million, the size of Croatia or Panama. Though dominated by HTS, the SSG has been somewhat politically inclusive, and several non-HTS leaders have had key roles in its administration.

It sought to include the independent governance councils that had arisen organically during the early days of the anti-Assad rebellion, and it established local municipal managers to provide essential services across its territory.

HTS’s small combat groups operated like a fast-moving light cavalry force. Picture: Omar Haj Kadour / AFP

American analysts in 2020 assessed the SSG as technocratic, “post-jihadi”, focused on internal stability and non-ideological governance, seeking acceptance from Turkey and the US, and unlikely to become a launch pad for external attacks.

Aaron Zelin – the Western expert most familiar with HTS and the author of an important book on the organisation, The Age of Political Jihadism – has observed that despite still holding extremist beliefs, HTS acts more like a state than a jihadist group.

While the SSG was focusing on social services and economic activity, HTS commanders were investing in advanced military capabilities. Building on experience from before the 2020 ceasefire, HTS organised its forces into small combat groups of 20 to 40 fighters that could mass quickly to swarm a target using several teams, or disperse to avoid enemy airstrikes or artillery.

They were highly mobile, operating like a fast-moving light cavalry force, mounted in a mix of hard and soft-skinned vehicles that included captured armoured vehicles and armed pick-up trucks (known as technicals).

Reconnaissance teams, scouts and snipers moved in civilian cars or on motorcycles. HTS combat groups carried heavy and light weapons including rocket launchers, captured artillery pieces, mortars, recoilless rifles, anti-tank missiles and Soviet-bloc small arms seized from the government or rival resistance groups including Islamic State.

Rebel fighters stand next to the burning gravesite of Syria’s late president Hafez al-Assad at his mausoleum in the family’s ancestral village of Qardaha. Picture: Aaref Watad / AFP

HTS also used the ceasefire to professionalise itself, studying the wars in Ukraine, Gaza and Lebanon. It established a military academy to educate officers in “military art and science”, and created civil affairs units, humanitarian agencies and a specialised organisation to convince government supporters to defect.

It used drones for reconnaissance, for leaflet drops on regime-controlled areas and as one-way attack munitions to strike targets with explosive warheads. It manufactured weapons and drones, and modified technicals with additional armour. HTS leaders built intelligence networks and command-and-control systems while allegedly also forging relationships with regional intelligence services and special operations forces.

Thus, the strength of HTS was not unexpected in itself. On the other hand, the rapidity of the regime’s collapse – which accelerated dramatically after the fall of the central Syrian city of Hama on the evening of Thursday, December 5, Syria time – was startling. It probably should not have been. Governments, unlike resistance movements, are tightly coupled complex systems that rely on numerous institutions and organisations, all of which must work together for the state to function.

As Joseph Tainter showed in The Collapse of Complex Societies, once co-ordination begins to break down, these interdependent systems unravel, the collapse of each brings down the next, and the entire structure falls apart. For this reason, in a process familiar to practitioners of irregular warfare, resistance groups (which tend to be loosely structured and thus more resilient to chaos) degrade slowly under pressure – and rebound once it is relieved – whereas governments collapse quickly and irrevocably once initial cohesion is lost.

As a team led by Gordon McCormick showed in a seminal 2006 study, governments that are losing to insurgencies reach a tipping point, after which they begin to decay at an accelerating rate. The conflict then seems to speed up and the end “is typically decisive, sudden and often violent”.

This pattern was very noticeable during the fall of the Afghan republic in 2021, for example, which also occurred in an 11-day period. The final Taliban offensive captured every province but one, and took the capital, Kabul, in a series of victories between August 4 and 15, 2021. Many garrisons surrendered, fled without fighting or changed sides.

Initial rebel successes made the regime look weak, allies failed to offer support, the security forces defected and other rebel groups suddenly rose up across the country. Picture: Aaref Watad / AFP

To be sure, the Taliban’s final campaign was built on years of coalition-building and insurgent warfare. Similar to HTS, the Taliban relied on patient construction of parallel networks largely illegible to an Afghan state increasingly alienated from, and seen as illegitimate by, its own people.

It also was enabled by a stunningly shortsighted political deal with the US in 2020 and an incompetent US-led withdrawal in 2021. Even so, the collapse of the Kabul government was faster than expected, with president Ashraf Ghani fleeing by helicopter in a manner remarkably similar to Bashar al-Assad’s exit last weekend.

The fall of South Vietnam in 1975 was likewise extraordinarily rapid, occurring in just nine days after the decisive battle of Xuan Loc, with South Vietnam’s last president, Nguyen Van Thieu, fleeing for Taiwan on a military transport plane.

Similarly, Fulgencio Batista’s government in Cuba fell in only five days, between December 28, 1958 – when a rebel column under Che Guevara captured the town of Santa Clara – and the early hours of January 1, 1959, when Batista fled by aircraft to the Dominican Republic. He had announced his resignation to shocked supporters a few hours earlier at a New Year’s Eve party in Havana, starting a scramble for the airport.

In Syria’s case, beyond these general dynamics of government collapse, something else was happening: a military version of what political scientists call a “preference cascade”.

As Timur Kuran, originator of the concept, points out, under repressive regimes (or ostensibly democratic ones that censor dissent) the gap between public pronouncements and private opinions increases over time, until many individuals dissent from the approved narrative and lose faith in institutions that promote it but remain reluctant to reveal their real views. This “preference falsification” creates a deceptive impression of consensus. It can make regimes believe they have more support than they really do, while convincing dissidents they are all alone so there is no point expressing a contrary opinion.

But when an unexpected shock reduces the regime’s power to suppress dissent, people suddenly feel empowered to express their real opinions. They realise these opinions are widely shared and the false consensus evaporates. This can trigger a “preference cascade”, where individuals or institutions suddenly change sides and support for the government collapses overnight.

In particular, the moment when security forces, particularly police, refuse to fire on protesters is often decisive, as seen in the fall of the Suharto government in 1998, the overthrow of Hosni Mubarak in 2011 or the collapse of the East German regime in 1989.

Kuran’s initial work centred on the East European revolutions of 1989, which were unexpected at the time but seemed inevitable in retrospect, something Kuran later came to see as inherent in revolutionary preference cascades.

The most extreme case was the fall of Nicolae Ceausescu in Romania. During a mass rally on December 21, 1989 the dictator suddenly realised, his face on camera registering utter shock, that what he had initially perceived as shouts of support were actually calls for his downfall. When his security ser­vices refused to fire on the protesters, Ceausescu was forced to flee by helicopter. Four days later, he and his wife Elena were dead, executed after a brief military trial.

A woman poses for a photograph with a rebel fighter’s gun in Umayyad Square in Damascus. Syria’s population finally felt free to dissent from the dominant narrative. Picture: Chris McGrath/Getty Images

Syria this week was another example of a preference cascade. Initial rebel successes made the regime look weak, allies failed to offer support, the security forces defected and other rebel groups suddenly rose up across the country. Syria’s population – previously reluctant to express anti-regime sentiment for fear of repression or social ostracism – finally felt free to dissent from the dominant narrative. Assad lost control, was forced to flee, and his government collapsed. It is worth briefly recounting the sequence of events.

On November 27, the HTS offensive began with a sudden attack on Aleppo City. The outskirts of Aleppo are only 25km from the HTS stronghold in Idlib, so although the outbreak of violence was a surprise, there was little initial panic. The regime responded with airstrikes and artillery, with Russian warplanes in support.

The first major shock was the fall of Aleppo on November 30, after three days of heavy fighting. As Syria’s second largest city, scene of a bloody urban battle in 2012-16, Aleppo’s sudden collapse was a huge blow to the government. The HTS capture of Aleppo airport, east of the city, denied the regime a key airbase from which to strike the rebels, and cut the highway to northeast Syria. At this point the regime seemed capable of containing HTS, though clearly under pressure, and there was still relatively little panic.

But then on December 4, HTS attacked the city of Hama, which fell on the evening of December 5. This was a huge leap forward – Hama is 140km south of Aleppo down Syria’s main north-south M5 highway, meaning the rebel forces had covered a third of the distance to Damascus in a week. The fall of Hama was another political and psychological blow to Assad’s regime: Hama had never been under rebel control at any time since 2011.

Syrian rebel fighters at the town of Homs, 40km south of Hama, a critically important junction controlling the M5 and the east-west M1 highway that links Damascus and central Syria to the coast, and dominating Syria’s heavily populated central breadbasket. Picture: Aaref Watad / AFP

The collapse at Hama – and the perception of regime weakness this created – triggered a preference cascade. Immediately, commanders began negotiating with or surrendering to the rebels or evacuating their positions. Also, after Hama’s fall, Iranian forces negotiated safe passage and began withdrawing from Syria, denying the government one of its key allies, further weakening Assad’s credibility, and encouraging yet more supporters to defect.

The regime’s other main ally, Russia, had already retreated to its bases at Khmeimim and Tartous, on Syria’s Mediterranean coast, after losing large amounts of military equipment and a still-unknown number of casualties. The same day, Hezbollah declined to offer material assistance to the Syrian government, given that it was still under Israeli pressure and had taken significant damage in 66 days of conflict.

The town of Homs lay 40km south of Hama – not much closer to Damascus but a critically important junction controlling the M5 and the east-west M1 highway that links Damascus and central Syria to the coast, and dominating Syria’s heavily populated central breadbasket. By early Friday, December 6, HTS combat groups were massing to assault Homs, but the city’s defences collapsed and it fell without a significant fight. By this point, security forces were dispersing, some retreating to Damascus but many fleeing to coastal areas.

The fall of Hama and Homs in quick succession encouraged other rebel groups to pile on, with several now mounting their own offensives against the regime. Uprisings broke out in the southern cities of Daraa and As-Suwayda on Friday and Saturday, December 6 and 7. These were less of a shock than the loss of Hama – Daraa was, after all, the cradle of the revolution in 2011 – but given everything else that was happening, the government simply lacked the forces to suppress them.

Simultaneously, US-backed forces in the far south advanced north from their base at al-Tanf, near the Jordanian border, while US-allied Kurdish troops of the Syrian Democratic Forces attacked in the east, crossing the Euphrates and seizing regime-controlled territory near Deir Ezzour. American aircraft flew airstrikes to support the SDF, which also seized the border post at Bou Kamal, blocking access to Iraqi militias that had been crossing into Syria to support the regime.

By this point – last Saturday evening, December 7, Syria time – the government was on its last legs. That night an uprising broke out in Damascus, launched by civilian resistance groups and disaffected military units keen to distance themselves from the regime as the rebels closed in. Government troops began abandoning their posts, changing into civilian clothes, ditching their equipment and disappearing into the night. Large numbers of armoured vehicles, including T-72 tanks, were abandoned in the streets of the capital. Assad had planned to address the nation that evening but did not appear.

Later that night, apparently without asking Assad, the high command of the Syrian armed forces issued an order to all remaining troops to lay down their weapons and disperse. Assad fled about 2am on Sunday, flying out in a Russian transport aircraft. Assad’s prime minister, Mohammed al-Jalali, announced that he was willing to act as caretaker during transition to a provisional government, showing that Syria’s civil government, like the regime’s military forces, had collapsed. Despite initial reports that Assad’s aircraft had been denied entry into Lebanese airspace then shot down over Homs, Russian media reported later on Sunday that he had arrived in Moscow.

By Sunday, the regime had completely collapsed and the rebels, led by HTS commander Ahmed al-Sharaa, formerly known as Abu Mohammed al-Jolani, occupied Damascus without a fight.

The same day, US aircraft mounted dozens of airstrikes across the country, targeting Islamic State or regime forces, while Israeli troops crossed the Golan Heights buffer zone and began advancing towards Damascus. By Monday, despite initially claiming their incursion was limited and temporary, Israeli forces were 25km from Damascus, Israeli politicians had announced the permanent annexation of the Golan, and Israeli aircraft were striking Syrian military bases and sinking Syrian ships at the Latakia naval base.

Israel has denied media reports that its troops have taken control of Syrian territory.

In addition to the Israeli incursion through the Golan, Turkish-backed troops of the Syrian National Army are attacking the SDF across a strip of northern Syria, apparently attempting to create their own buffer zone separating the SDF – which Ankara sees as allied to the Kurdistan Workers Party – from Turkish territory.

The SDF has seized a chunk of eastern Syria, other US-allied rebel groups hold key parts of the south, and Islamic State still has numerous supporters and active cells in the country. Russia still controls its two Syrian bases, while Syria’s ethnic and religious minorities including Christians and Alawites are deeply anxious about the future, despite promises of tolerance from HTS.

Given the speed and totality of Assad’s collapse, some observers seem to be assuming that HTS will now, by default, become the dominant player in Syria. On its face, this may seem a reasonable assumption, given what happened in similar situations – Havana 1959, Saigon 1975, Kabul 2021 and so on.

But it would be premature in Syria’s case since the war is very much ongoing. As the northern hemisphere winter closes in and Western allies prepare for a change of administration in Washington, Syria – along with Gaza, Lebanon, the Red Sea, Ukraine, Taiwan and the Korean peninsula – will remain a major flashpoint into the new year.

David Kilcullen served in the Australian Army from 1985 to 2007 and was a senior counter-insurgency adviser to General David Petraeus in 2007 and 2008, when he helped design and monitor the Iraq War troop surge.