Korea.
24
China was interested in Korea because they saw them as an important trading partner and also a military outpost. Japan was interested for them to open 3 ports to trade and also similar to China's reason. They then made a hands-off agreement saying that they would not send their armies to Korea.
Various Chinese Dynasties, Mongol Empire, and Empire of Japan
Korea
For their emperor and to expand their empire
After Japan took over Korea, Korea was treated badly. Even though Japan does not admit, Koreans were forced to speak Japanese, believe their religion, and many other Japanese customs. If not, they were executed or tortured. Japan also did many unfair things to Koreans such as scientific human tests, selling them as slaves, and destroying their monuments. The relationship between Japan and Korea is similiar to the relationship between Germany and Poland in WW2.
Japan had very limited arable land and resources. In the meantime, across the sea of Japan, a huge Chinese empire was falling apart. There were large oil, coal and iron ore deposit in Manchuria, located in north east China bordering Korea.
Centuries ago, Korea was part of China. From about 1900 until the end of World War 2, Korea was ruled by Japan.
The division of Korea was the result of the 1945 Allied victory in World War II ending the Empire of Japan's 35 years colonial rule of Korea by General Order No.1.
Hoping to expand their empire further, the Mongols launched two naval assaults on Japan, but were thwarted by hurricanes. The Mongol Empire expanded little after the creation of the Yuan Dynasty.
The neighboring countries of North Korea are South Korea, China, Russia, Japan, and Mongolia.