US President Donald Trump welcomed the fall of the Islamic State group's five-year "caliphate", but warned that the terror group remained a threat.
Mr Trump's remarks came after Kurdish-led Syrian Democratic Forces (SDF) raised victory flags in the Syrian town of Baghuz, IS's last stronghold.
He said the US would "remain vigilant until [IS] is finally defeated".
Despite losing territory in Syria and Iraq, IS remains active in countries from Nigeria to the Philippines.
At its height, the group controlled 88,000 sq km (34,000 sq miles) across Syria and Iraq.
After five years of fierce battle, though, local forces backed by world powers left IS with all but a few hundred square metres near Syria's border with Iraq.
On Saturday, the long-awaited announcement came from the SDF that it had seized that last IS territory. Western leaders hailed the announcement but emphasised that IS was still a danger.