Terrorists, acting in the name of Daesh or the Islamic State, attacked Britain three times in three months, targeting young girls and civilians on bridges and markets. Prime Minister Theresa May, her voice laced with frustration told the British public that “Enough was enough” and promised to do more. But: What more can she do? British intelligence services are already overwhelmed by the number of suspects that they track and monitor, and would need to triple or quadruple the number of agents they have in order to monitor the people on their list. Da’esh is losing territory in Iraq and Syria. The battle for Mosul is in its final stages. When it falls, Da’esh will no longer control a major city in Iraq. The capital Raqqa is now surrounded on three sides. The khilapha, or caliphate declared by the Islamic State, will not survive long when it no longer controls territory.

But Da’esh fighters are moving to Libya and Yemen, and some are returning home to Europe now that defeat seems imminent. They bring with them skills and anger at their defeat.

Is a new wave of terror attacks about to begin? It is hard to argue that the three attacks in Britain constitute a new wave, since British intelligence and police have disrupted 16 attacks since 2013.

Nobody is better equipped to grapple with that question than Joby Warrick, the author of the gripping new book, Black Flags: The Rise of ISIS. The

book won the Pulitzer Prize for General Non-Fiction in 2016. The Pulitzer jury described Black Flags as “a deeply reported book of remarkable clarity showing how the flawed rationale for the Iraq War led to the explosive growth of the Islamic State.”

Joby Warrick is a reporter for The Washington Post and the author of the 2011 best seller, The Triple Agent.