In this book, Clarke aims to cover what he calls “global jihadism,” although he primarily focuses on al Qaeda and the Islamic State (or ISIS). His account ends several months before ISIS lost the last of its territory with the fall of Baghouz, in Syria, in March of this year, but Clarke’s main message is that the jihadists will regroup in Iraq and Syria and that al Qaeda and ISIS will lead the way. What is more controversial, he argues that the launching of a caliphate by ISIS, in 2014, will in the end prove far more significant than its destruction. He does not add much to the existing literature on jihadism, and although he offers some intriguing figures, he does not explain them. There are some 230,000 jihadists worldwide, he says, but only 19,000 people on government terrorist watch lists. ISIS recruited around 43,000 fighters from 120 countries; between 6,000 and 11,000 of them may be left. In all, Clarke estimates that some 70,000 jihadists have been killed in recent years.