Middle East Analyst Rodger Shanahan has told DW that the speed with which the Assad regime fell surprised commentators and regional countries alike.
"Most people expected a much bigger fight to be put up and this to be a bloody campaign, but it turned out to be quite the opposite," he said.
He said the rebel forces were very well-prepared and motivated for the offensive, while the Syrian army had been "hollowed out over the years."
"The Assad military forces were not willing to fight and die for their cause, whereas the opposition were," Shanahan said, adding that the rebels gained momentum early on that was difficult to stop, beginning with the fall of Aleppo.
He said the speed of the offensive also meant that Assad's backers in Russia and Iran "weren't able to act quickly enough, and probably, given the lack of fight in the Syrian military, decided that they wouldn't react in the end."
Shanahan said also the rebels were at pains to ensure that civilian infrastructure remained as intact as possible to facilitate a smooth transition of power. Syria's rebel coalition said it was working to transfer power to a transitional governing body.
"The great Syrian revolution has moved from the stage of struggle to overthrow the Assad regime to the struggle to build a Syria together that befits the sacrifices of its people," it said.
Security analyst Rodger Shanahan said the announcement showed maturity among the rebel leaders.
DW journalist Gasia Ohanes said she expects the coming days to reveal the "horrors" of Bashar Assad's regime.
"In the next few days, we'll see a lot of the brutality and the horrors of the Assad regime will come to light," she said, pointing to "political prisoners who have been imprisoned for decades" and who have now been released.
She said Syrian army conscripts would leave the military, and displaced Syrians would also start returning home.
"We'll see soldiers who've been conscripted forcefully for 13 years now go back to their families," she said. "More than 12 million Syrian people have been displaced in this war — all of them will be trying to see how they can get back home [and] see their families."
Ohanes said that "so far we have not seen any signs" of attacks on minority groups such as Christians, Druze and Alawites.
Ohanes said the Hayat Tahrir al-Sham (HTS) rebel group has "changed [its] stance in recent days with this offensive and part of that could be to gain recognition later on from the international community," but noted that it is an extremist group that is classified by the United States and other nations as a terror organization.
She pointed out that in the northwestern city of Latakia, which is majority-Alawite and a traditional Assad stronghold, a statue of the ousted leader was toppled "without a single bullet being fired."
Iranian Embassy stormed by rebels
Rebels have stormed the Iranian Embassy in Damascus following their capture of the Syrian capital.
Footage from the AP news agency showed broken windows and documents scattered along the entrance to the embassy.
Iran, along with the Hezbollah militia it supports, and Russia were the main supporters of the Assad government. Their assistance helped the Syrian regime forces regain and maintain control of important parts of the country during the civil war and enabled Assad, apparently until now, to remain in power.
US to retain military presence in east to prevent IS resurgence: Pentagon official
The US military will maintain a presence in eastern Syria to keep terrorist group Islamic State (IS) in check, the Pentagon has said amid concerns that the organization might exploit the current unsettled political situation in the country.
Daniel B. Shapiro, a deputy assistant secretary of defense for the Middle East, said the US presence was "solely to ensure the enduring defeat of [IS] and has nothing to do with other aspects of this conflict."
"We are aware that the chaotic and dynamic circumstances on the ground in Syria could give [IS] space to find the ability to become active, to plan external operations," he said.
IS captured large swathes of territory in Syria in 2014-2015, exploiting the opportunities and power vacuums amid the Syrian civil war, but lost all its Middle Eastern territories by 2019 through conflicts with various forces, including those backed by the United States, such as the Kurdish-led Syrian Democratic Forces.
Since then, IS has reverted to relatively minor acts of insurgency, but fears remain across the region that it could engineer a return to power in some areas.
Shapiro made his remarks at the Manama Dialogue security conference in Bahrain's capital.