By Episode 4 - Beginning of the War:
This episode deals with the January 12, 1950 Press Club speech by US Secretary of State Dean Acheson which left Korea out of the United States’ “defense perimeter”. Also is an explanation of the North Korean preparations for war. Stalin forces Mao to sign a defense treaty with North Korea. The May 1950 South Korean elections. John Foster Dulles visits the 38th Parallel. The United Nations Commission visits the 38th Parallel to make sure war would not break out (June 1950). The start of the North Korean attack (June 25th). The North Koreans blame the South for starting the wider conflict.
1:03 pm on July 17th, 2009 1
Based on David Halberstams book, (yes, I forgot the name) there were many signs of impending war, to include the rebuilding of many bridges and railheads all along the border, that would have no other purpose than an invasion from the north to the south. Many of these signs were ignored by MacArthur and his staff.
Atchesons speech which was supposedly misinterpreted was probobly interpreted correctly at the time, as no political consensus by the US government as to what would be done with korea had been reached. He just reiterated where the US was at that time. A signal that NK would be allowed to attack with no US support was a misinterpretation on the part of North Korea and Moscow.
At the same time Kim Il Jong was actively planning an invasion with the support of Stalin. (Altho' Stalin was somewhat reluctant to go along, he did provide tanks and aircraft as well as military supplies).
China has also been implicated, since the war, as providing significant numbers of veteran Chinese troops of Korean ethnic background to North Korea at this time . (Any argument that China entered the war only to protect its borders is lost with its assistance in the original invasion)