Board Thread:Questions and Answers/@comment-3550280-20130813130442/@comment-3398633-20130813135329

It is indeed possible. Remember, Muslim converted most of Indonesia by the 1300s, and as the island traded extensively with China, which was the protector of Korea, with whom the Muslims also traded with, it is entirely possible for them to have converted the population if given the chance. Christianity is the second largest religion in Korea because the Church was more aggressive in conversion that the Muslims, which means they put forth more effort to convert the population, while the Muslim depended on conversion by will, as is often the case today. If can explain why the Muslims made a more concerted effort in converting Korea like the Church did, then you can theoretically create an Islamic Korea. The Muslims aren't far away either, so you have plenty of plausibility on your side.