Korea was once a part of the Japanese empire and according to older members of the Korean community in São Paulo* the Japanese governor outlawed Korean martial arts and promoted Kendo and Judo at schools. Korean Kendo is known a Kumdo.
Koreans are also crazy about archery, shooting and badminton, sports in which they generally go well.
*I used to live in "Bom Retiro" neighborhood in São Paulo which is a center of the Korean community here, they said me that exactly.
Korea was only a Japanese colony for 35 years (1910-1945). After the Japanese occupation ended, the Koreans did their best to reject everything Japanese, so I don't think you can base your conclusion on that.
I don't deny that the Koreans do well in other sports, just that it's not like they have a cultural advantage or something. For example, their dominance in archery at the 2008 games was partially due to their building an exact replica of the Beijing archery range in Korea 2 years earlier and using it to practice. Many other competitors had never practiced on that archery range until they arrived at the Olympics, and it threw them off.
Don't know, a Korean friend said Kumdo is one of the most popular sports in Korea, he lived there for a couple of years, don't know about judo but I would not be surprised if it was that popular as well.
I'm not Korean and only said what members of the Brazilian-Korean community, in which I have a some friends, said to me.
Koreans are also crazy about archery, shooting and badminton, sports in which they generally go well.
*I used to live in "Bom Retiro" neighborhood in São Paulo which is a center of the Korean community here, they said me that exactly.