Historical development of military intelligence as a discipline and institution, organized by period. Each entry traces the intelligence methods, institutional forms, and conceptual innovations of its era.
- Ancient and medieval intelligence — from Sun Tzu’s agents through Roman frumentarii, Byzantine intelligence, and medieval espionage
- Early modern intelligence — Walsingham’s networks, Richelieu’s cabinet noir, the emergence of organized state espionage
- Nineteenth century — the Great Game, the professionalization of military intelligence, the birth of signals interception
- World War I — Room 40, the Zimmermann Telegram, aerial reconnaissance, and the first institutionalized intelligence services
- Interwar period — the Black Chamber, Enigma preparation, the fragmentation of American intelligence
- World War II — Ultra, the OSS, Soviet wartime intelligence, the transformation of intelligence from craft to institution
- Cold War — the CIA, KGB, Mossad; SIGINT, satellite reconnaissance, HUMINT; the discipline’s mature form
- Post-Cold War — 9/11, Iraq WMD, the intelligence reform era, the rise of cyber and open-source intelligence
For the genealogical relationship between Puritan covenantal culture, Harvard, and the U.S. intelligence community, see Puritan Covenants, Harvard Yard, and the Making of U.S. Intelligence.