You have wrong thought. Korea was independent country.

Japan invade Korea. They invaded Korea at 1592. Japan have bellicosity .

culture flows from China through Korea to Japan in Middle Ages.

Korea were Chinese slave for a long time. All Koreans were poor, even upper classes were filthy dirty. Korea presented women to China from the Middle Ages. Japan stopped all disgusting Korean tradition.
Korea demanded merger to Japan. They threatened Japan even assassinating the Japanese PM Hirofumi Ito. Japan annexed Korea unwillingly to prevent invasion of Russia and China.
However, we have been looking after Korea for long enough. Japan poured two-thirds of national assets and did Manchurian and Korean infrastructure maintenance. Meanwhile, Japanese citizen was forced to very frugal living. Only Japan gave education to all of them. There were Korean teachers, government officers, army officers. Chinese and Korean woman did not have the name. Only Japan gave them the name.

After the end of the war, the Korean betrayed Japan. And they pretend to be the Japanese victim. Many Japanese are still murdered and raped by them now. Japanese children attempted murder by Korean is happening in Japan, United States and Korea.
Koreans always lay the blame on Japanese. So, We get tired of that and not trust them anymore.