Following World War II, the United States hoped that global security could be managed collaboratively by the victorious allies using a network of international organizations, particularly the newly created United Nations. But it quickly became clear that the Soviet Union would be an adversary, not a partner. Initially, U.S. policymakers disagreed on how to respond to the mounting Soviet threat. Great power strategy was new to Americans, something they had to learn on the fly. Neither placating nor threatening Moscow seemed to work.
In 1946, Department of State official George Kennan, an astute student of statecraft and history, offered a solution. First in a telegram sent from his diplomatic post in Moscow and later in an article for the influential journal Foreign Affairs, he explained that the Soviet Union's version of communist totalitarianism, like the czarist system that preceded it, had deep flaws. If it did not expand it would collapse. Kennan thus advocated "a policy of firm containment, designed to confront the Russians with unalterable counterforce at every point where they show signs of encroaching upon the interest of a peaceful and stable world."
Kennan did not invent the idea of containment. It has been used by states throughout history when the benefits of defeating or ameliorating a threat did not justify the expected costs, and when the state undertaking it felt that time was on its side. The idea is that if a problem is not allowed to spread, eventually it will be easier to deal with or go away on its own.