The Japanese invasion force was comprised of 160,000 regular army troops, 80,000 bodyguard troops, 1,500 heavy cavalry, 60,000 reserve troops, 50,000 horses, 300,000 firearms 500,000 daggers, 100,000 short swords, 100,000 spears, 100,000 long swords, 5,000 axes, and 3-4,000 boats (40-50 feet by 10 feet). The army was also supported by another 700 ships, transport vessels, naval ships, and small craft manned by 9,000 seamen. Having been acquainted with the use of firearms since 1543, the Japanese had imported a large number of muskets from Europe, and had developed the ability to manufacture them four years before the first invasion.
The Koreans, on the other hand, had few firearms and did not know how to use or manufacture them. Outnumbered and armed only with swords, bows and arrows, and spears, the Korean military was severely disadvantaged in the face of the Japanese invading army armed with 300,000 muskets. Although a few courageous Korean units resisted, such as those under the command of General Kim Si-Min, the army of Japan reached Seoul in just 15 days and occupied the entire country by May 1592.
The Korean king, Son Jo, fled with his court to Uiju in the Northern Provinces with permission from the Ming emperor of China with whom the Koreans had several treaties. When the Ming armies joined in the fight, the tide of the war shifted away from the Japanese. They had to fight Korean guerilla groups as well as the Ming army, while at the same time finding themselves cut off from their supplies by Admiral named Yi Sun-Sin. Disease, malnutrition, and the cold soon took its toll on Japanese morale. Having lost the will to fight, retreating Japanese forces were stalked by guerilla forces led by Confucian scholars and Buddhist monks. Peace negotiations eventually took place between the Ming general and the Japanese, but these talks dragged on for five years and reached no conclusion.