The X Article, formally titled "The Sources of Soviet Conduct", was published in Foreign Affairs in 1947. Though signed pseudonymously by "X," it was well known at the time that the true author was George F. Kennan, the chief of mission to the USSR from 1944 to 1946. The article is famous because it set forth the doctrine of containment.
Primary source
Fulltext of "The Sources of Soviet Conduct (http://www.historyguide.org/europe/kennan.html)
For us, the LongTelegram has more immediate relevance, for what cannot be debated is that within the final three paragraphs—a mere three hundred and fifty words—is America’s survival guide for dealing with the security challenges of the twenty-first century.
Long wars usually centralize power in the state and in the long run diminish it by crushing innovation, stifling liberty, and inefficiently employing resources.
The Soviets were, he pointed out in the LongTelegram, “by far the weaker force.” Thus, Kennan argued that it was critical that the United States not overreach and unnecessarily diminish itself against an enemy that could not win in the long term.
The LongTelegram was perhaps the most cited and most influential statement of the early years of the Cold War.
The essence of Kennan's telegram was published in Foreign Affairs in 1947 as The Sources of Soviet Conduct and circulated everywhere.
As long as remnants of capitalism were officially recognized as existing in Russia, it was possible to place on them, as an internal element, part of the blame for the maintenance of a dictatorial form of society.