The fall of Assad in Syria creates a security vacuum – and may give Donald Trump little choice but to play a role

The lightning collapse of Bashar al Assad’s regime in Syria exposes the brittleness of even the most brutal dictatorship when under pressure, but it also creates a security vacuum that carries great risk.

Once the scenes of rebel euphoria subside on the streets, much will rest on the powerful group, Hayat Tahrir al Sham (HTS), which led the charge into Damascus overnight.

Previously linked to al Qaeda, this Sunni Islamist militant faction is viewed as a terrorist organisation by many Western powers, including the UK.

But the movement has sought to distance itself from its extremist roots and instead emphasise a commitment to tolerance of minorities.

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Now, having achieved such stunning success over the past few days, its leader Abu Mohammed al Jolani faces the even bigger task of uniting a country that has been divided by civil war for more than 13 years.

The Assad regime, which comes from Syria’s minority Alawite sect of Shia Islam, inflicted terrible violence on its people, in particular during the first years of the uprising that began in 2011 – and including the use of chemical weapons.

Bringing those responsible to justice without resorting to violent retribution will be a key, though hugely difficult, test for whether a transition of power led by HTS can be relatively peaceful.

Even with the best intentions of the HTS leadership, though, Syria has become a breeding ground for Sunni Islamist terrorism – and this threat could grow.

Any security vacuum will be exploited by Islamic State – which formed a caliphate across swathes of Syria and Iraq during the early years of the civil war – and by al Qaeda.

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Putin must be in crisis mode

Then there is the question of Mr Assad’s foreign backers, primarily Russia and Iran.

Vladimir Putin must surely be in crisis mode following the sudden vanquishing of an ally he had previously successfully propped up when rebel groups first challenged his grip on power.

Russia has two strategic military facilities on Syria’s Mediterranean coast – the Tartus naval base and the Hmeimim airbase in Latakia province.

Both will be under threat unless the Kremlin is able to cut some hasty deal with Syria’s emerging powerbrokers – though such a move would surely be near-on impossible given Moscow’s part in supporting the violence carried out previously by Mr Assad’s army.

The dramatic transformation in the reality on the ground will be felt even more starkly by Iran, whose forces have similarly been instrumental in supporting the regime, both through the Islamic Revolutionary Guard Corps (IRGC) as well as Iranian-backed Hezbollah forces in Lebanon.

Syria has been a key part of an axis of influence cultivated by the IRGC over decades and has been an important site for smuggling weapons to Tehran’s proxy forces across the region.

Turkey could emerge as an important ally

Other regional powers will also be rapidly reassessing their approach to Damascus.

Turkey, which shares a border with Syria, will be an interesting nation to watch.

President Recep Tayyip Erdogan’s government has long strongly opposed Mr Assad and has been an important backer for a number of rebel groupings that helped to oust him.

It means Ankara could well emerge as an important ally to the new Syrian leadership.

Trump may be left with little choice

The United States, which has been supporting a Kurdish rebel group in the northeast of Syria, has been unusually muted during the past week of unprecedented change.

President elect Donald Trump has been clear he does not see a role for Washington in the crisis.

But should the situation descend into escalating bloodshed once again, he may have little choice.