A new branch of history has arisen: the study of intelligence. Not that the topic has ever been ignored. In most decades of this century, some scholars referred to intelligence, their works augmented by a few semi-official accounts and a good many bad books. Diplomatic and military historians often discussed espionage and used it for purposes of evidence or explanation. In Russia and the Balkans, 1870–1880 (1937), for example, B. H. Sumner integrated intelligence and diplomacy as well as any subsequent writer. Meanwhile, beginning in the later nineteenth century, the genre of spy fiction began to flourish. Old-hands-turned-hacks like Somerset Maugham, Ian Fleming, and E. Howard Hunt shaped that genre and general views about espionage: They publicized the secret services.

The number of works, scholarly and popular, that referred to intelligence began to rise around 1960; in the early 1970s began a flood. The decision of Her Majesty's Government to release some – not all – of its records about “Ultra” during the Second World War transformed public attitudes as “Magic” never had. So, too, did the era of angst in the United States that culminated in the Watergate scandal. The secret world suddenly seemed central to the real world. It also became accessible to the public. Much material about contemporary American intelligence was released through congressional committees, while the number of journalists interested in the field and old hands willing to speak about their careers increased.