There are an estimated 9 to 10 million Presbyterian Christians divided amongst 100 different denominations out of a population of 51.7 million in South Korea. How did a branch of Christianity originating in Scotland become the faith of nearly 1 in 5 South Koreans today?

/u/ARPK has previously answered What accounts for the prevalence of Christianity in South Korea?

/u/dsk_oz has previously answered Why did Christianity grow in South Korea after WWII to the point that now a third of the country is Christian...?

More answers remain to be written. This question has come up multiple times. None of the related answers specifically talk about Presbyterians, so hopefully another redditor will be able to address that part of your question.