The Korean peninsula had been occupied by Japan from 1910 . On August 9 , 1945 , in the closing days of World War Two , the Soviet Union declared war on Japan and advanced into Korea . Though the Soviet declaration of war had been agreed by the Allies at the Yalta Conference , the US government became concerned at the prospect of all of Korea falling under Soviet control . The US government therefore requested Soviet forces halt their advance at the 38th parallel north , leaving the south of the peninsula , including the capital , Seoul , to be occupied by the US . This was incorporated into General Order No. 1 to Japanese forces after the Surrender of Japan on August 15 . On August 24 , the Red Army entered Pyongyang and established a military government over Korea north of the parallel . American forces landed in the south on September 8 and established the United States Army Military Government in Korea
Yalta Conference
Yalta Conference
North Korea–South Korea relations