In George Kennan's "Long Telegram" (1946), what are the primary arguments? How did he explain the threat of the Soviet Union and communism? How did he characterize the weakness of the Soviet system? And how does he suggest that the United States should respond to the perceived threat of the Soviet Union's communism?

George F. Kennan was an American Foreign Service officer serving as the Charge d'Affaires in Moscow when he sent the so-called "Long Telegram" to the U.S. State Department on February 22, 1946. It was roughly 8,000 words long, and it suggested a U.S. policy of containment to counter the aggressive policies of Stalin's Soviet Union.
Kennan wrote that the Soviet Union was deeply insecure and suspicious. He wrote:

At bottom of Kremlin's neurotic view of world affairs is traditional and instinctive Russian sense of insecurity.

Because of this innate suspicion, the Soviets believed that ultimate security could only be achieved by the "total destruction of rival power." Kennan warned that the Soviets were intent upon expansion and that they would most likely begin with Iran and Turkey. They would also seek to weaken the influence of Western powers on "colonial areas and backward or dependent peoples." He wrote:

In general, all Soviet efforts on unofficial international plane will be negative and destructive in character, designed to tear down sources of strength beyond reach of Soviet control. This is only in line with basic Soviet instinct that there can be no compromise with rival power . . .

Kennan wrote that the weakness of the Soviet system was that it did not work by fixed plans and was mainly negative and destructive. He concluded that, as a result, it was "highly sensitive to logic of force." This prompted the Truman administration to rely on the threat to US economic and military forces—rather than diplomacy—in dealing with the Soviet Union.
Kennan closed his telegram with a recommendation to take a calm, long-term approach to the Soviet problem. He suggested studying the nature of the communist movement, educating the American people on the "realities of Russian situation," and solving internal problems of American society so that it could remain strong. In conclusion, he wrote:

Finally we must have courage and self-confidence to cling to our own methods and conceptions of human society. After all, the greatest danger that can befall us in coping with this problem of Soviet communism is that we shall allow ourselves to become like those with whom we are coping.
https://history.state.gov/departmenthistory/short-history/kennan

https://nsarchive2.gwu.edu/coldwar/documents/episode-1/kennan.htm

https://www.history.com/this-day-in-history/george-kennan-sends-long-telegram-to-state-department