Timeline of Korean War: 1950 - 53
End of WW2 - Korean peninsula occupied by US forces in South+USSR forces in North, divided by 38th Parallel which was agreed in Potsdam
1 - In June 1950, NK invades SK in an attempt to seize it's territory: UN (led by US) intervenes for South's side but Seoul quickly falls, by mid Sep, NK occupies all but small corner around Pusan in South
2 - NK advance in Sept 15 1950
3 - UN counterattacks in Sept 1950: US led forces (officially UN soldiers) led by American general Douglas MacArthur landed at Inchon in SK and drove NK back to 38th Parallel