I have this theory for a while that the exceptional brutality and war crimes of Imperial Japan to their Asian neighbors are a direct result of demonic influence through their State Shinto religion. And we obviously know as Orthodox that pagan deities are fallen spirits. Japan's defeat and subsequent occupation by America removed this capability of widespread destruction by their militant polytheism, but this godlessness and degeneracy simply manifested itself in other ways in modern Japanese society.
On the other hand, Christianity has been the most successful in Korea because the demonic influence in their lands and culture is less compared to their neighbors. The Korean Peninsula also enjoyed far longer periods of peace and stability compared to Japan and China; however, the drawback was that Koreans didn't develop a martial culture which meant they got steamrolled by external invaders every single time (e.g. the Mongols during the Goryeo Dynasty or Hideyoshi invading Joseon).
What's more interesting, however, was that Korean scholars took the initiative to be catechized into Catholicism during the 1700s, starting with a Korean envoy in Qing China. American Protestant missionaries also enjoyed success in Korea starting in the late 1800s, and ironically most of the Korean Christian population before 1945 was located in the north, and Pyongyang was known among Western missionaries as the "Jerusalem of the East."
Christianity also served as a platform for Korean nationalism during the 35-year rule of Imperial Japan. The Japanese built Shinto shrines in Korea and compelled Koreans to worship the Emperor of Japan as a deity. Of course, many Koreans resisted because it would mean submission to a foreign occupier. However, Christians in Korea (both Korean converts and American missionaries) also saw it as an act of idolatry, and thus refused to worship in the shrines, resulting in many churches being persecuted. The establishment of Communist rule in northern Korea forced many Korean Christians to flee to the south; in the decades after the Korean War, Christianity also stood for anti-Communism and support for democracy.