Mohammed Emwazi isn’t the only westerner who has joined ISIS. About 5,000 fighters in Syria and Iraq come from Europe, North America, or Australia. Just yesterday, three men were arrested in Brooklyn on charges that they planned to carry out attacks here and then join ISIS in Syria. And it’s not only men becoming radicalized. Earlier this week, London police said three teenage British girls suspected of running away to join ISIS have likely made it to Syria. Why has ISIS been so successful at recruiting men and women from western cities?