On five trips to Iraq, Rukmini Callimachi and a team of other New York Times journalists scoured files and other papers left behind by the Islamic State, which help explain how the so-called Caliphate had been able to stay in power there for a number of years. The impression left behind? That ISIS’s penchant for brutality is matched by its acumen for efficient bureaucracy. All manner of infrastructure was apparently maintained better under the group than it had been under the Iraqi government. Money was raised not only through the sale of stollen oil, but through agriculture and through well organized and enforced taxation. Callimachi covers this in an interactive piece.