How did lessons learned from world war 2 influences president Truman's decision to send troops to aid south Korea after north Korea invaded?

In World War II, the Allies appeased Hitler when he began invading surrounding countries and allowed him to gain power before war was declared on Germany, leading to a horrific and drawn out war. Truman did not want to make the same mistake and allow North Korea to cause immense damage due to his failure to act soon enough.