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If you may know, Korea for too long a had been a society and government entrenched in Neo-Confucianism, and was servile to China while being hostile to other nations. Make a scenario where the Koreans start to believe that they are the true upholders of Confucianism and stop having the Sino-centric attitude they had for many centuries. The POD would preferably be in the 1700s.
This will help: Neo-Confucianism in Korea Korean Sinocentrism Mandate of Heaven