"The Sources of Soviet Conduct", commonly "X Article", is an article written by George F. Kennan and published under the pseudonym "X" in the July 1947 issue of Foreign Affairs magazine. It introduced the term "containment" to widespread use and advocated the strategic use of that concept against the Soviet Union. It expanded on ideas expressed by Kennan in a confidential February 1946 telegram, formally identified by Kennan's State Department number, "511", but informally dubbed the "long telegram" for its size.
Kennan composed the long telegram in response to inquiries about the implications of a February 1946 speech by Joseph Stalin. Though the speech was in line with previous statements by Stalin, it provoked fear in the American press and public; Time magazine called it "the most warlike pronouncement uttered by any top-rank statesman since V-J Day". The long telegram explained Soviet motivations by recounting the history of Russian rulers as well as the ideology of Marxism–Leninism. It argued that the Soviet leaders used the ideology to characterize the external world as hostile, allowing them to justify their continued hold on power despite a lack of popular support. Washington bureaucrats quickly read the confidential message and accepted it as the best explanation of Soviet behavior. The reception elevated Kennan's reputation within the State Department as one of the government's foremost Soviet experts.