Since the Islamic State has suffered losses over the past two years in more conventional military operations, the extremist group is now focusing on guerilla warfare and terrorism, said Daniel Byman, a professor at Georgetown University’s Walsh School of Foreign Service.

“We’ve already seen the number of foreign fighters going to Iraq and Syria decline. From the Islamic State’s point of view, these are desperate attacks. But they are successful in their own right and do indicate that we will see more attempts,” said Byman, also a senior fellow at the Center for Middle East Policy at the Brookings Institution.

He added that the more desperate the Islamic State becomes, the more the group, also known as ISIL or ISIS, will rely on amateurs.

“ISIS has tens of thousands of individuals that are scattered not just in the Middle East but also to West Africa, to Southeast Asia, and beyond,” CIA Director John Brennan told the Council on Foreign Relations last week.