Short answers, pulled from the story.
The X Article refers to The Sources of Soviet Conduct published anonymously in Foreign Affairs magazine in July 1947. It outlined the strategy of containment against Soviet expansionism and became a foundational text for United States Cold War policy.
George F. Kennan wrote the Long Telegram on the 22nd of February 1946 while serving as chargé d'affaires in Moscow. This document stretched over 5,000 words and analyzed Soviet behavior to justify a new American foreign policy approach.
Kennan chose to publish the article anonymously because government restrictions prevented him from writing under his own official name at the time. He later revealed the authorship after the article gained widespread attention following its publication in July 1947.
Walter Lippmann responded with fourteen columns starting the 2nd of September 1947 which were collected into the book Cold War. He criticized the article for presenting strategic monstrosity and claimed it gave Soviets initiative in any conflict.
Joseph Stalin delivered a speech at Moscow's Bolshoi Theatre on the evening of the 9th of February 1946 that alarmed American officials and prompted Kennan to analyze Soviet intentions. This speech led directly to the creation of the Long Telegram and eventually the anonymous X Article published in Foreign Affairs magazine.