Ever since Korea and Japan established kingdoms in the 6th century, both countries greatly influenced each other politically, militarily, socially, culturally, and economically through international exchange. Korea and Japan kept their close relationship throughout history because of geographic proximity. It is also notable that 54 per cent of Japanese males and 66 per cent of Japanese females carry Sino-Korean genes in present-days and there are records that Japan carried a close relationship with Paekche, a kingdom of the Korean peninsula which introduced script, Confucianism, and Buddhism to Japan at an early stage. In the Medieval Period, Korea and Japan maintained a friendly trade policy but there were incidents such as Mongol invasions, wakō (Japanese pirates) raids and two invasions by Toyotomi Hideyoshi, which worsened the relations between the two countries. And yet, during Japan’s period of isolation (from 1639 to1854), Korea was the only nation with which full and free trade was permitted. The 20th century is based on invasion and colonisation of Japan over Korea. For 35 years from 1910 to 1945, under the control of Japan, the Japan-Korea relationship was nothing but misfortune: forced labour, suppression of Korean culture and language, press-gangs, sex slaves, and so forth. The aim in this thesis is to go into greater detail about each significant event and its effect on the relationship between Japan and Korea to uncover some rationale or pattern such as gekokujō (the master being outdone by the pupil, and being treated thereafter with contempt).