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Machiavellianism is a Diplomatic Policy Card in Civilization VI.
Strategy
Machiavellianism provides both a 
Production bonus when training Spies and a reduction in the time it takes Spies to complete their missions; however, it will not change the duration of missions that have already started. Therefore, one can adopt this policy before commencing Spy operations and drop the policy afterwards without penalty.
Civilopedia entry
By definition “Machiavellianism” is “the employment of cunning and duplicity in statecraft” (in psychology it is defined as one of the dark triad personalities, but that’s another thing). In his works The Art of War (1521 AD) and The Prince (1532), Machiavelli advocated that effective rulers routinely employ espionage, deception, and assassination to insure their interests … which were the interests of their state, of course. While a number of kings took his advice to heart, it was Queen Elizabeth’s “spymaster” (actually he was the Secretary of State) who developed the best Renaissance spy network, employing linguists, scholars, authors, engineers, soldiers, and diplomats to seek out and analyze secrets (both internal and external).