What was a cause of the korean war (1950-1953)?

On 25th June 1950, ninety thousand North Korean soldiers invaded South Koreas border defences, The Korean war had begun, this small scale civil war would escalate into an international conflict. Historically Korea had once been a united country, under Japanese rule for between 1905 and 1945 however, the Japanese were unruly and did not treat the Koreans well. At the end of the Second World War it was decided that the country would be divided along the 38th parallel and occupied by soviet troops in the North and American troops in the South. Syngman Rhee, who had spent some years exiled in America, became the president of South Korea in 1948, while Kim Il Sung, having fought for the Russian red army during the war became leader of the Peoples Democratic Republic (Communist) in North Korea. I intent to outline the causes and contributing factors that eventually led to the Korean War.