Hayat Tahrir al-Sham (HTS), the militant group that has seized control of Aleppo and parts of Hama in a surprise offensive, has a complex history in Syria's long-running conflict.

Originally established in 2011 as the terror group Jabhat al-Nusra, it began as an Al Qaeda affiliate and has since evolved into one of Syria's most powerful opposition forces against the government of Basher Al-Assad, which failed to defeat the opposition in the north of the country since the majority of fighting stopped some years ago.

The group's origins are tied to both Al Qaeda and ISIS, with ISIS leader Abu Bakr al-Baghdadi involved in its initial formation. Under its original name, Jabhat al-Nusra quickly gained a reputation as one of the most effective fighting forces against President Bashar al-Assad's government, though its jihadist ideology set it apart from the mainstream Syrian opposition.

A significant shift came in 2016 when the group's leader, Abu Mohammed al-Jawlani, publicly split from Al Qaeda. The organisation rebranded as Hayat Tahrir al-Sham after merging with several other militant groups in 2017.

Since then, HTS has focused on establishing fundamentalist Islamic rule within Syria and removing the Al-Assad regime, rather than pursuing the broader international jihadist agenda of groups like ISIS.

Before its recent offensive, HTS had consolidated its power in Syria's northwestern Idlib province, where it operates as the de facto government for approximately four million people, many of whom are displaced Syrians from other regions.

However, the group's attempts at legitimate governance have been marred by allegations of human rights abuses, as witnessed in recent days of attacks on Kurds and Christian-owned liquor shops.

The timing of HTS's current offensive appears strategic. Recent Israeli strikes have weakened Iranian-backed militias in Syria, including Hezbollah, which have been crucial to Assad's military success. These groups, along with Russian air support, had been essential in compensating for Syria's stretched and poorly motivated conscript army.

With Assad's Iranian-backed allies weakened, HTS launched its largest offensive in years, quickly seizing large parts of Aleppo - Syria's second-largest city and a former rebel stronghold lost to government forces in 2016.

The surprise attack has prompted the first Russian airstrikes on Aleppo since 2016 and forced a Syrian military withdrawal from the city.

The offensive marks a dramatic shift for HTS, which had shown little indication of attempting to reignite the Syrian conflict on such a scale but has now been met with fierce response from Syrian government forces, Iraqis militias, Russia and Iran’s IRGC.

While the group maintains control of Idlib under a 2020 ceasefire agreement brokered by Russia and Turkey, its latest actions suggest broader territorial ambitions.

This resurgence comes at a time when Syria's conflict had appeared largely settled, with Assad's rule going essentially uncontested in major cities for the past four years. The success of HTS's offensive not only challenges this status quo but also raises questions about the stability of Assad's government without consistent support from its traditional allies.