WWII
During WWII and the Japanese campaign in west Asia creating puppets over preexisting countries and spreading their power over "inferior" nations. The Japanese spread their conquest to the Korean peninsula around 1905 and quickly began to resonate their power. The Japanese asserted their power by forcing the Koreans to do hard labor, some became sex slaves, and others their slaves. They quickly banned the teachings of the Korean language and burned almost all government documents.
Ending Japanese Expansion
At the Yalta Conference, which was held in February 1945, allied leaders discussed how to end the war and how to restore the previously Japanese controlled nations, along with much more. Joseph Stalin, the Soviet leader, along with President FDR agreed to occupy north and south Korea respectively at the 38th parallel in order to liberate Korea. Later on in the war following President FDR's death, President Harry Truman and party made the decision to drop the atomic bomb on the city of Nagasaki. In the following days after the bomb was dropped Soviet forces invaded from the north in an attempt to get rid of the Japanese. The Japanese regime surrendered to the allied powers following another atomic bomb drop on Hiroshima ending WWII. The next month American armed forces invaded Korea from the south.
Conflicting Powers
The United States and Soviet Russia were at disagreements for many years due to political differences. One nation being communist whilst the other being democratic, the two could not agree on a single governing system throughout Korea. The United States set up a democratic administration in the South Korean capital of Seoul which after many rigged elections, came under power of Syngman Rhree. Rhree was very ruthless leader, but the United States favored him because of the simple fact, he supported democracy. The Soviets were angered and retaliated by forming a communist delegation under leadership of Kim Il-Sung, an almost equally ruthless leader. Both leaders would imprison and slaughter whole families if they had the slightest assumption a member believed in the opposing ideologies. The two governments did not respect each other and did not acknowledge each other of existing and attempted to spread ones influence. By the year 1949, the troops previously sent to liberate Korea were withdrawn. Since the beginning of creating a communist regime int he north, the Soviets encouraged the Kim Il-Sung to grow their military. Soon, there was an imbalance of military powers on the Korean peninsula. On June 25, 1950, the North Korean government attempted to reunify Korea and launched an attack across the 38th parallel, witch approval from the Soviets. This distinctive act would go down in history as the beginning of the Korean War.