How did lessons learned from World War 2 influence President Truman's decision to send troops to aid South Korea after North Korea invaded?
One of the main things that Truman was concerned about was any type of escalation, he hoped the war would remain limited to the Korean peninsula and in order to make sure that happened he kept a tight limit on the amount and scope of troops that would be committed. There was also the backing of the United Nations that was important as they tried to make it appear an international effort in order to avoid conflict with the Chinese or the Soviets.
Some lessons were not learned, however, as the troops that were sent were often not properly equipped, particularly for the bitter cold they faced after the US troops pushed north towards the Yalu river. This was analgous to the lack of winter clothing for troops in WWII as planners hoped to save money and banked on the war being over before the winter of 1944.