“At long last, the Assad regime has fallen,” President Joe Biden said in a speech from the Roosevelt Room of the White House. The president’s remarks on Sunday followed the news that President Bashar al-Assad’s government had fallen to rebel forces who united from across the nation against the brutal dictator.

“This regime brutalized and tortured and killed literally hundreds of thousands of innocent Syrians,” Biden said. “The fall of the regime is a fundamental act of justice. It’s a moment of historic opportunity for the long-suffering people of Syria to build a better future for their proud county. It’s also a moment of risk and uncertainty.”

Biden announced that the U.S. military had conducted air strikes in Syria to keep the Islamic State from claiming power in Assad’s absence. Assad is currently wanted for war crimes over deadly chemical weapons attacks on the Syrian people.

Assad had lost some backing from his allies — Iran, Russia and Hezbollah — which gave rebel fighters the opportunity to topple his regime.

Those allies were “weakened and distracted” by other global events, leaving Assad “basically naked,” National Security Adviser Jake Sullivan said Saturday before the rebel groups arrived in Damascus, according to ABC News.

“Over the last week, their support collapsed, all three of them, because all three of them are far weaker today than they were when I took office,” Biden said of Syria’s allies, adding, “The upshot of this is for the first time ever, neither Russia nor Iran nor Hezbollah could defend this horrible regime in Syria.”

Donald Trump weighed in on the conflict earlier this weekend, writing on X that the situation was a “mess” and the U.S. should stay out of the conflict.

“In any event, Syria is a mess, but is not our friend, & THE UNITED STATES SHOULD HAVE NOTHING TO DO WITH IT. THIS IS NOT OUR FIGHT. LET IT PLAY OUT. DO NOT GET INVOLVED!” Trump wrote.

While Biden was triumphant about Assad’s defeat, he cautioned that the U.S. will keep close watch on what the rebel groups do next.

“We will remain vigilant,” Biden said. “Make no mistake, some of the rebel groups that took down Assad have their own grim record of terrorism and human rights abuses.”

Biden continued, saying the rebels are “saying the right things now,” adding, “But as they take on greater responsibility, we will assess not just their words, but their actions.”

Biden also commented on Austin Tice, an American journalist and Marine veteran who has been held in Syria for more than 12 years, when a reporter asked about Tice as Biden was leaving the room.

“We believe he’s alive. We think we can get him back,” Biden said.

“We are eagerly anticipating seeing Austin walk free,” his parents, Marc and Debra Tice, said in a statement obtained by The Washington Post. “We are asking anyone who can do so to please assist Austin so he can safely return home to his family.”