United States in the Korean War At the conclusion of World War II the Allied nations began the process of disarmament of Axis controlled regions . Japan occupied Korea at this time and had been in control since 1910 . In 1945 the decision was made to have American military forces oversee Japanese surrender and disarmament south of the 38th parallel and the Soviet Union would facilitate the change of power to the north . At the time there was no political motivation and seemed to be a logical and convenient plan of action . The original agreement and intent was to create a unified and independent Korea out of the post Japanese occupation era . Instead each side of the 38th parallel established its own government under the influence of the occupational country ; the United States in South Korea and the Soviet Union in North Korea . Both new Korean governments discredited the other and claimed to be the only legitimate political system . Tensions between the North and South escalated and each side began to petition foreign powers for resources and support . South Korea wanted weapons and supplies from Truman and the United States government while North Korea sought help from Stalin and the Soviet Union . The United States was still war weary from the disruptive World War II campaign and refused South Korea ' s request for weapons and troops . North Korea convinced the Soviet Union to supply them with the weapons and support they requested . This decision coincided with the United States withdrawing the last remaining combat troops from South Korea . North Korea saw its opportunity and attacked South Korean forces at the 38th parallel on June 25 , 1950 and thus initiating the Korean conflict . Initial response . In response to North Korea ' s invasion into South Korea the United Nations convened to formulate a response . The U . N , demanded North Korea ' s immediate with drawl and when this was not met United States Army General Douglas MacArthur was appointed supreme commander of U . N . forces . To halt the rapid progress of North Korean forces into the south Task Force Smith was deployed to the Korean front from Japan . Task Force Smith consisted of U . S . Army officers and regiments of the Army ' s 24th Infantry Division that were stationed in Japan as occupational forces . Unfortunately the 24th were under trained , poorly supplied , and outnumbered . The 24th offered very little resistance against the North Korean advance . American and South Korean troops were pushed south and in late July 1950 Task Force Smith was overrun in the city of Taejon . Troops from the Army ' s 25th Infantry Division were deployed to Taejon to establish a new line and pullout the decimated 24th I . D . This addition of combat troops did not stop the North Korean advance and both American and South Korean troops were pushed further south . Battle of Osan . The first battle the Americans entered in the Korean War was the Battle of Osan , where about four hundred strong landed in Pusan airport on the first of July . The American troops were warmly welcomed by the residents and were sent off to Taejon the next morning where Major General John H . Church the head of U . S . field headquarters was confident in the US troop ' s strengths to push back the North Koreans . On July fifth the troops were finally put to the test when North Korean tanks crept towards Osan . The four hundred infantryman of the U . S . also called Task Force Smith opened fire on the North Koreans at 8 : 16 am . Only four of the North Korean tanks were destroyed and twenty - nine kept moving forward breaking the US line . At the end of the battle only two more North Korean Tanks and two regiments of North Korean infantry were destroyed . The US had lost the battle , revealing that the mere sight of US troops would not reverse the military balance in Korea . By early August , the North Korean troops had pushed back the US and South Korean troops all the way to Naktong River , which is located about thirty miles from Pusan . The two weeks of fighting following this resulted in the most casualties of US troops than any other equivalent period of this war . However , during this time the US pushed supplies and personnel to Korea and by the end of July South Koreans and US troops outnumbered the North Koreans , although the North had pushed back the US and South by an amazing amount the North had lost over fifty thousand casualties . Also because North Koreas supply lines were so lengthy and with the US in control of the water and air replenishing there losses were slow . Inchon . Although MacArthur clearly stating that it was a 5000 to 1 gamble , it was an important military move to make . Inchon is 25 miles from Seoul on the coast and only once during September is the water even deep enough to allow the 29 foot draft of American LSTs . It was a defenders best place to allow troops onto Korea , and to push invaders back . On September 15 the battalions off US army stormed Korea , by the end of the night over a third of Inchon was taken back .