In the aftermath of the attacks on Paris that left more than 120 people dead, there’s been a rush to lay blame on everything from the refugees fleeing the Middle Eastern countries overrun by the Islamic State to the French government’s relations with Belgium.

At least five of the attackers have been identified as French nationals, indicating that one of the biggest dangers to French citizens is homegrown terrorism, and nationals who identify with ISIL. Still, a host of American state governors and European politicians have said they will refuse to take Syrian refugees.

Quartz spoke to Rohan Gunaratna, the head of the International Centre for Political Violence and Terrorism Research in Singapore, about the root causes of the attacks, the rise of the Islamic State, and how governments around the world should combat terrorism.

Gunaratna is one of Asia’s most prominent terrorism experts, and has been studying the root causes of political violence and extremism since the Sept. 11, 2001 attacks on the United States. He is a former fellow at the Combating Terrorism Centre at the United States Military Academy at West Point, a professor of security studies at the S. Rajaratnam School of International Studies in Nanyang Technological University, Singapore, and has served as a counter-terrorism instructor for government special forces.