Traditionally, spies have been defined as "secret agents of a State sent abroad for the purpose of obtaining clandestinely information in regard to military or political secrets." Older authorities have stated emphatically that the gravamen of espionage is the employment of disguise or false pretense. Such deception has been the justification for visiting the severest of penalties upon the captured spy. Curiously, however, the employment of spies has not been considered reprehensible conduct. The refusal to officially acknowledge the commissioning of a spy operated to relieve the government of any responsibility either to the offended state or to the secret agent. As a result, espionage in the classic sense can be characterized in two distinct ways: as to the nation, it was an extraterritorial act of state for which the state was not responsible; as to the agent, it was an intentional act of deception which rendered him personally and criminally liable to the offended government.
The industrial revolution of the past century coupled with the rapid technological advancement of the present have placed great strains on the definition, as well as on the dual nature, of espionage. Beginning at least as early as the Franco-Prussian War of 1870, the concept of control of information began to weigh heavily in the minds of those responsible for national security.
Leslie S. Edmondson,
Espionage in Transnational Law,
5 Vanderbilt Law Review
Available at: https://scholarship.law.vanderbilt.edu/vjtl/vol5/iss2/13