Perhaps the scariest thing about Frontline’s excellent new edition The Secret History of ISIS is that the history of the terrorist group isn’t all that secret. Secret History focuses on Abu Musab al-Zarqawi, who is repeatedly referred to be various interviewees here as a “thug” who rose with alarmingly easy quickness to overtake Osama bin Laden as the world’s most prominent formentor of global terrorism. Frontline traces the way Zarqawi’s quick, lethal, down-and-dirty methods–untethered from much of the religious posturing and personal myth-making that bin Laden indulged in–enabled him to grow ISIS into a frightening force that soon overtook al Queda in the minds of millions and in the media.