• The ISIS files.

On five trips to battle-scarred Iraq, New York Times journalists scoured old Islamic State offices in 11 cities and towns, gathering thousands of documents abandoned by the militants as their “caliphate” crumbled.

Following a paper trail that led through booby-trapped streets near the front lines of battle, they found suicide bomber forms, birth certificates, tax records, school books teaching English words like “gun” and “martyr,” and papers from the Ministry of War Spoils. (Here’s a closer look at the documents.)

The records reveal how the terrorist group combined brutality and paperwork to wield power over territory that at one point was the size of Britain, with a population estimated at 12 million people.