The 38th parallel, the temporary military demarcation line drawn by the US and the Soviets, became a political boundary separating the South and the North. North Korea quickly built its military power. By the time the Soviets completed their withdrawal from the North in October 1948, the North had fully equipped 4 infantry divisions and an armored battalion, the 105th, equipped with Soviet T-34 medium tanks. A secret military treaty between the North and the Soviets was signed in March 1949. Additionally, the mutual defense treaty of March 18 between North Korea and China resulted in transferring 25,000 Korean military personnel under the Chinese Communist forces to the North. The North was soon able to station 10 divisions of 130,000 soldiers along the demarcation line and complete its military reserve system of 100,000 soldiers. Believing in its superiority in military power coupled with the international political climate at the time, Il-sung Kim dreamed of armed unification of the South and North.
International factors favoring the North to attack the South were:
1) Establishment of Communist China in October 1949.
2) The withdrawal of US forces in June 1949.
3) The announcement by Acheson D.G., US Secretary of State in January of 1950 when he announced that Korea and Taiwan would be excluded from the US security perimeter in January 1950.
4) Getting the approval of Stalin for an all-out armed attack by the North against the South during Il-sung Kim’s visit to Moscow at the end of 1949.
Domestic factors favoring the North to attack the South were:
1) Collapse of the ‘Namro Party’ making it almost impossible for any chance of a ‘People’s Revolution’ in South Korea.
2) Il-sung Kim’s need to override Hon-young Park as the fighter for the people.
3) Political and economic disorder in the South.
4) South Korea’s inferiority in military power.
Embarking on his dream of armed unification, he passed a resolution through his party for armed re-unification of Korea in early April of 1950. In order to hide the plan to invade, the North started peace campaigns which included a proposal to hold a South-North Unification Supreme Legislation Conference in Seoul and to re-unify Korea through the efforts of the legislative bodies of the South and North.
In comparison, South Korea, although its manpower reached 100,000 by 1949 following the re-organization of the National Defense Forces and the Coast Guard under US Trusteeship into the Army and Navy respectively in 1946 and the establishment of the Marine Corps in April of 1949 and the Air Force in October of the same year, its military was poorly equipped and incomparably inferior to that of the North. In addition, without any military reserve system, 4 divisions of the 8 existing were stationed far from the demarcation line working on mopping up the communist guerrillas.