NEXT on FRONTLINE: How did the American invasion of Iraq and the decisions of two presidents help lay the groundwork for ISIS? "The Secret History of ISIS" shows how Zarqawi developed what would become the ISIS playbook right under the U.S. government's nose. Watch on PBS June 20, or anytime online. http://to.pbs.org/21aH7Zt | FRONTLINE | PBS

The fight against ISIS is literally door-to-door in Mosul, Iraq, where civilians fear not only the terrorists, but also the Iraqi army. When an army unit enters this home, watch as the family shakes in fear of the very men who are supposed to protect them. Catch “Hunting ISIS” streaming online, anytime: http://to.pbs.org/2kFfqMk | FRONTLINE | PBS