As to who did in reality fire that shot, Bruce Cumings, head of the history department at the University of Chicago, gave us the definitive answer in his two-volume The Origins of the Korean War, and The Korean War: A History: the Korean war started during the American occupation of the South, and it was Rhee, with help from his American sponsors, who initiated a series of attacks that well preceded the North Korean offensive of 1950. From 1945-1948, American forces aided Rhee in a killing spree that claimed tens of thousands of victims: the counterinsurgency campaign took a high toll in Kwangju, and on the island of Cheju-do – where as many as 60,000 people were murdered by Rhee’s US-backed forces.
Rhee’s army and national police were drawn from the ranks of those who had collaborated with the Japanese occupation during World War II, and this was the biggest factor that made civil war inevitable. That the US backed these quislings guaranteed widespread support for the Communist forces led by Kim IL Sung, and provoked the rebellion in the South that was the prelude to open North-South hostilities. Rhee, for his part, was eager to draw in the United States, and the North Koreans, for their part, were just as eager to invoke the principle of "proletarian internationalism" to draw in the Chinese and the Russians.
Having backed the Maoists during World War II, in cooperation with the Soviet Union, the US had already "lost" China, and Truman was determined not to "lose" Korea, too. In spite of the fact that he had ample warning of the North Korean offensive, the President used this "surprise attack" to justify sending American troops to Korea to keep Rhee in power, and in doing so neglected to go to Congress for approval – or even give them advance notice.
http://original.antiwar.com/justin/2013/07/28/who-really-started-the-korean-war/
