United States of Jihad tells the story of several American citizens (out of several hundred investigated by the author) who committed terrorist attacks in the US and overseas. Some are well-known, like the Tsarnaevs brothers who struck at the Boston marathon, others almost anonymous. It also describes the efforts of law enforcement to catch and ideally prevent would-be terrorists from acting in the first place.
The book is in turn chilling and reassuring. Chilling because it seems quite easy to gain the skills to build bombs or plot attacks. Chilling, also, because the authorities appear at times comically unable to follow up on leads and use the systems in place properly. But most of it is strangely reassuring, as large-scale terrorist operations find it very challenging to continue to operate under scrutiny.