What Turns a Skater Kid from Colorado into a Fighter for ISI

Tens of thousands of men and women have left comfortable, privileged lives to join the Islamic State of Iraq and Syria—and kill for it. The highest-ranking American currently fighting for ISIS is John Georgelas, a Texan whose dad was a US Air Force colonel. Who are the Westerners who join ISIS? Where do they come from? What do they believe? And most importantly, what can we do to stop them?