In a speech at the University of Texas at Austin this week, FBI Director James Comey again warned of the coming ‘terrorist diaspora’ that will ensue following the collapse of ISIS in Iraq and Syria.

The Islamic State has attracted an unprecedented amount of international support since its inception in 2014. Tens of thousands of foreigners from over 100 countries around the world have been inspired by their jihadi vision, and traveled to Syria and Iraq to take part.

Director Comey warns that once their territory is “crushed” those thousands of fighters will flow out of the country, into Europe, Africa, and Asia in numbers never before seen. Comey noted that the exodus of fighters will be akin to the aftermath of the Soviet-Afghan War, when mujahedeen who had fought for a decade in Afghanistan left the battlefield to continue the jihad abroad.

Al-Qaeda, led by Osama bin Laden, got its start during this period.

Director Comey noted that while ISIS has had its recruiting efforts interdicted since 2015, helping to stem the flow of inspired followers onto the battlefield in the Middle East, the archetypal ISIS influence remains the homegrown “lone wolf” style attack. The United States and Europe have seen numerous accounts of individuals, radicalized through the internet by ISIS propaganda, planning and executing their own attacks without support from the terror network.

On Wednesday, a British citizen named Khalid Masood used a vehicle to attack pedestrians on a bridge in London, and then fatally stabbed a British Police Officer near Parliament. He was subsequently shot and killed by police.

Initial reports from the British government indicate they believe he was inspired by radical Islamist propaganda from ISIS.

Director Comey has in the past sought to frame the conflict with ISIS as a protracted battle, and this is the second time he has publicly spoken of a ‘terrorist diaspora’ that the world must prepare for.