The military invasion launched by Toyotomi Hideyoshi of Japan against Korea from 1592 to 1598, which also brought China into the conflict at a later stage, had a far-reaching impact on the course of East Asian history. The genesis of the invasion dates from the time when, as Hideyoshi's goal of achieving a national unification of Japan was nearing completion, he openly expressed his desire to launch a military expedition against Korea and China for the purpose of territorial conquest. Such a venture abroad would also give a convenient outlet to the excess energies of the Japanese warriors. Hideyoshi apparently hoped to win Korea's support for his military venture, but when his demand that his troops be allowed to pass through Korea on their way to invade China was refused, he ordered his forces of more than 158,000 men to attack Korea in April 1592.
The first contingent, commanded by Konishi Yukinaga, landed at Pusan on 23 May and quickly overran the fortress of Tongnae. Soon thereafter, other Japanese troops rushed to Korea. Korea was woefully ill prepared to meet the Japanese invasion. The diplomatic mission sent to Japan in 1590 returned with conflicting reports on the possible intent of Hideyoshi toward Korea. The peace Yi-dynasty Korea had enjoyed for two centuries, coupled with the pacifist sentiment of Neo-Confucian idealism, had left Korea totally unprepared for military crisis. Japan, on the other hand, showed military superiority on land in all aspects. The Korean defenders were especially helpless against the firearms the Japanese employed. Thus, as the Japanese troops advanced along the three main routes toward Seoul, Korea could offer little effective resistance. In desperation, the Yi court-pinned its hopes on General Sin Ip to halt the Japanese in a gallant but hopeless stand at T'an'gumdae, outside Ch'ungju. When the news of General Sin's defeat reached the capital the king and his court fled, to the taunts and jeers of an angry crowd. On 12 June, only twenty days after the initial landing, the Japanese occupied Seoul. After a brief pause, they pushed northward, Konishi seizing P'yŏngyang in July and Katō Kiyomasa leading his troops into Hamgyŏng Province. Driven to the border town of Ŭiju, the Korean court finally appealed to Ming China for military assistance.
As the initial shock of defeat began to wear off, Korea was able to put up more effective resistance. On sea, along the southern coast, Admiral Yi Sun-sin was achieving spectacular victories against the Japanese navy using his heavily armed "turtle" ships, thus interrupting Japanese supply and communication lines. On land, numerous militia units, known as the "righteous armies," were organized by the local gentry and Buddhist monks to fight the intruders. In the meantime, China, regarding the Japanese occupation of Korea as a threat to its own security, dispatched more than forty thousand troops, retaking P'yŏngyang in February 1593 and forcing the Japanese to retreat to the north of Seoul, where, at Pyŏkchegwan, the Japanese ambushed the Chinese. Not long thereafter, the regrouped Korean army, under the command of Kwŏn Yul, defeated the Japanese at the mountain fortress of Haengju, compelling the Japanese towithdraw to the south of Seoul. The military situation now reached a stalemate, forcing negotiations between China and Japan.
The negotiations followed circuitous routes amid trickery and misunderstanding until 1597. Hideyoshi's demands included the marriage of a Chinese princess to the Japanese emperor, the restoration of tally trade, and the cession of four southern provinces of Korea. Hideyoshi's negotiators misled him about the Chinese response to these demands, and he was astonished and enraged to find that the Chinese mission of "submission" was actually bearer of a document certifying him as king of Japan and a vassal of the Ming emperor. A second invasion was mounted in August 1597. In the temporary absence of Yi Sun-sin, who was in disfavor, the Japanese navy fared better. This time, however, the Japanese were met by more effective resistance from the allied armies of Korea and China, and the Japanese advance was stopped near Seoul at Chiksan. There was now growing awareness among the Japanese commanders of the futility in further bloodshed. The sudden death of Hideyoshi in September 1598 provided a convenient excuse to withdraw all the Japanese troops from Korea.
The war was extremely costly for Korea in both human and material terms. Korea lost innumerable cultural and artistic treasures, and the war left bitter scars of fear and resentment in the minds of the Koreans toward Japan. Ming China also suffered greatly as the costly war weakened its control over the border region, allowing the Manchu tribe to gain strength. Japan, on the other hand, benefited in cultural terms. The Neo-Confucianism of Zhu Xi was transmitted to Japan, Japan acquired the technique of movable-type printing, and a large-scale relocation of Korean ceramic artists enabled Japan to enrich its ceramic industry with porcelain ware.