What diplomatic and strategic errors led to the Korean War?

Answer 1

As with all wars, there were numerous factors in play, both on the Korean Peninsula and on the world stage. Some of the decisions made can be seen as, and may have been, errors.

• The decision by two politically opposite nations to invade Korea and set up a government was probably the first of these. The US and the USSR agreed to invade the Korean Peninsula to expel the Japanese at the end of WW2. The US was to invade from the south while the USSR invaded from the north, with both stopping at the 38th parallel. Once WW2 was over, each facilitated the establishment of a government which met their political ideals. With the two ideologies being polar opposites, it was just a matter of time until there was conflict.
• Another "error" was made by then US Secretary of State Acheson, who stated in his National Press Club speech on January 12, 1950 that the US Pacific defense perimeter was a line from the Philippines to the RyuKyu Archipelago to Japan to the Aleutian Islands. This statement may have sent the wrong signal to Kim Il Sung (Premier of the Democratic People's Republic of Korea) and Joseph Stalin.
• Kim Il Sung may have believed that the UN, backed mainly by the US, would not respond to the invasion with military force. He evidently didn't factor in the absence of the USSR from the UN Security Council.
• The USSR, which was protesting the Chinese seat on the Security Council, which was at the time held by the Republic of China, not the People's Republic of China, was not present at the UN Security Council meeting which adopted UN Security Council Resolution 82. If Stalin had sent an envoy to the UNSC, he could have vetoed the resolution.