As I recall, an important US official stated that Korea was not inside the US defense sphere; we weren’t interested in it. That is what provoked the invasion. I think it was the secretary of defense.
This is what bothers me about having incompetent people at any level of government. One poorly chosen statement can cost thousands of lives. There should be a special school for officials. It should teach them to never speak to the press, period. Only official, sanctioned sources should ever speak to the press.
It was Dean Acheson and he was the Secretary of State.