History of espionage

Spying, as well as other intelligence assessment, has existed since ancient history. In the 1980s scholars characterized foreign intelligence as "the missing dimension" of historical scholarship." Since then a largely popular and scholarly literature has emerged. Special attention has been paid to World War II, as well as the Cold War era (1947–1989) that was a favorite for novelists and filmmakers.

Efforts to use espionage for military advantage are well documented throughout history. Sun Tzu, 4th century BC, a theorist in ancient China who influenced Asian military thinking, still has an audience in the 21st century for the Art of War. He advised, "One who knows the enemy and knows himself will not be endangered in a hundred engagements." He stressed the need to understand yourself and your enemy for military intelligence. He identified different spy roles. In modern terms, they included the secret informant or agent in place, (who provides copies of enemy secrets), the penetration agent (who has access to the enemy's commanders), and the disinformation agent (who feeds a mix of true and false details to point the enemy in the wrong direction to confuse the enemy). He considered the need for systematic organization and noted the roles of counterintelligence, double agents (recruited from the ranks of enemy spies), and psychological warfare. Sun Tzu continued to influence Chinese espionage theory in the 21st century with its emphasis on using the information to design active subversion.

Chanakya (also called Kautilya) wrote his Arthashastra in India in the 4th century BC. It was a 'Textbook of Statecraft and Political Economy' that provides a detailed account of intelligence collection, processing, consumption, and covert operations, as indispensable means for maintaining and expanding the security and power of the state.

Ancient Egypt had a thoroughly developed system for the acquisition of intelligence.^{[citation needed]} The Hebrews used spies as well, as in the story of Rahab. Thanks to the Bible (Joshua 2:1–24) we have in this story of the spies sent by Ancient Hebrews to Jericho before attacking the city one of the earliest detailed reports of a very sophisticated intelligence operation.

Spies were also prevalent in the Greek and Roman empires. Kataskopes graphe (κατασκοπῆς γραφή) was a legal action in ancient Athens specifically targeting spies. If a foreigner was caught engaging in espionage, they could be prosecuted under this action. The accused spy was often subjected to torture, typically by being placed on the rack, to extract information. Following this, they were typically executed. Athenian citizens who were guilty of espionage were prosecuted for prodosia (προδοσία, meaning treason), a different charge under Athenian law. Trials for prodosia were typically conducted before the Athenian assembly, and the punishments for those found guilty were severe. The standard penalties included execution, the loss of the right to be buried in Attic soil (a significant dishonor), and the confiscation of the individual’s property. In some cases, lesser forms of prodosia or related offenses may have been recognized and punished with fines.

During the 13th and 14th centuries, the Mongols relied heavily on espionage in their conquests in Asia and Europe. Feudal Japan often used shinobi to gather intelligence.

A significant milestone was the establishment of an effective intelligence service under King David IV of Georgia at the beginning of the 12th century or possibly even earlier. Called mstovaris, these organized spies performed crucial tasks, like uncovering feudal conspiracies, conducting counter-intelligence against enemy spies, and infiltrating key locations, e.g. castles, fortresses and palaces.

Aztecs used Pochtecas, people in charge of commerce, as spies and diplomats, and had diplomatic immunity. Along with the pochteca, before a battle or war, secret agents, quimitchin, were sent to spy amongst enemies usually wearing the local costume and speaking the local language, techniques similar to modern secret agents.