In a lightning-quick two-week campaign that shocked the world, the Syrian Rebels led by the Islamist group Hayat Tahrir Al-Sham toppled Syria's longtime ruler Bashar al-Assad.
President Joe Biden cautiously welcomed Assad's removal on Sunday, calling it a “moment of historic opportunity”.
With Assad gone, the stakes are high for the US, and analysts warn that it must work carefully to achieve its goals in the region and avoid the country collapsing into chaos.
Burcu Özçelik, senior fellow on Middle East security at the UK think tank Royal United Services Institute, said Assad's defeat provides the US with an opportunity to continue its long-standing goal of breaking Iran's regional power.
„With the ouster of Assad, Iran was dealt a strategic blow, fulfilling the overarching US objectives of reducing and destroying Iran's so-called axis of resistance," she said.
But Chris Doyle, director of the Council for Arab British Understanding, says that since the Arab Spring of 2011. The US has had no diplomatic relations with Syria and its role in the country in recent years has been largely limited. This means that the US is still thinking about how to handle the situation.
When Syria's civil war broke out in 2011, it quickly turned into a brutal power struggle between rebel militias, government forces and their powerful foreign backers, including the US, Turkey, Iran and Russia, Businessinsider wrote in its analysis.
The US has provided training and support to some rebel groups, notably Kurdish militias and moderate groups, but has not directly intervened in the conflict.
When the Islamic State militia took over parts of northeastern Syria in 2014. and used it as a base for terrorist attacks in the West, the US led an international campaign to destroy the group.
But it has played a fairly limited role in the country since then, with about 900 troops in the northeast tasked with rolling back IS operations and protecting the US' Kurdish allies.
This could limit the ability of the US to play a larger role now.
Andreas Krieg, a specialist on the Persian Gulf at the Institute of Near East Studies at King's College London, said the US would likely limit its role to a "low-level campaign" fighting ISIS until a new authority is established in Syria.
One of the US's key goals will be to help restore order, protect its allies and prevent another brutal power struggle between rival militias and religious groups that could spill over into neighboring countries.
According to Mohammed Albasha, founder of the Basha Report, a Virginia-based consultancy specializing in Middle East affairs, the end of Assad's rule has left a "significant security vacuum" which extremist groups could use to regroup and expand.
Russia also suffered a defeat by ousting Assad.
Russian forces played a key role in halting rebel advances when Russia entered the conflict in 2015. According to reports, Assad and his family have taken refuge in Moscow.
With Assad gone, Russia may have lost access to strategically vital military bases in Syria.
There has been speculation over who will take over in the vacuum left by Assad's ouster. Among the key contenders is Abu Mohammad al-Jolani, the leader of the Hayat Tahrir al-Sham militia, which played a central role in defeating Assad and who fought alongside an al-Qaeda affiliate during the US occupation of Iraq.
HTS — a militant group designated as a terrorist organization by the US and UN controls Syria's northwestern Idlib province, where analysts say it has worked to consolidate power and transform its image as it pursues its ultimate goal of ousting Assad.
„The designation of HTS and al-Jolani's own legacy of violence in Iraq against US troops as a terrorist makes him far from an ideal partner for peace from the perspective of Western politicians," said Yozcelik.
In a post on Sunday, President-elect Donald Trump said the US should stay out of the conflict.
Yaniv Voller, senior lecturer in Middle East politics at the University of Kent, said it was hard to see how Washington could work directly with al-Jolani unless he completely abandoned his jihadist rhetoric and hostility to Israel.
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„Jolani has been associated with Al Qaeda and for most of his 'career' has expressed staunchly anti-American and anti-Western views," he said, adding that it was risky if Syria penetrated into territories controlled by rival militias and warlords, which would make the country a potential base for terrorist activities. From the US point of view, it would be much worse.