South Korea in and of itself was of little importance to the global balance of power, but the fact that it had been invaded so blatantly—across the 38th parallel, a boundary sanctioned by the United Nations—appeared to challenge the entire structure of postwar collective security. It had been just this sort of thing that had led to the collapse of international order during the 1930s, and to the subsequent outbreak of World War II. Truman hardly needed to think aboout what to do: “We can’t let the UN down,” he reportedly told his advisors. It took the administration only hours to decide that the United States would come to the defense of South Korea, and it would do so not just on its own authority, but under that of the United Nations as well.

What It Means

This is a placeholder explanation generated by the low-overhead model. It interprets "South Korea in and of itself was of little importance to the global balance of power, but the fact that it had been invaded so blatantly—across the 38th parallel, a boundary sanctioned by the United Nations—appeared to challenge the entire structure of postwar collective security. It had been just this sort of thing that had led to the collapse of international order during the 1930s, and to the subsequent outbreak of World War II. Truman hardly needed to think aboout what to do: “We can’t let the UN down,” he reportedly told his advisors. It took the administration only hours to decide that the United States would come to the defense of South Korea, and it would do so not just on its own authority, but under that of the United Nations as well." in the context of "John Lewis Gaddis, The Cold War: A New History (2005), p. 43" to mean that wisdom is timeless.