Following the establishment of the Goryeo kingdom, the Muslim presence in Korea would reach new heights. At first, it was mostly Arab traders flooding into the kingdom, but in the late Goryeo era, when Korea was dominated by the Mongol Yuan Dynasty, Muslims would come to Korea as soldiers and administrators, and the Muslim faith would begin putting down roots in the country.An update links to another article in English by Don Baker in Harvard Asia Quarterly entitled Islam Struggles for a Toehold in Korea. Here's the abstract.
Historical records show that in the early years of the Goryeo era, large Muslim — probably Arab — tribute delegations came to the Korean capital of Gaegyeong (present day Kaesong) in 1024, 1025 and 1037, presenting such rare gifts as mercury and myrrh. The Goryeo king prepared for these travelers special lodging and presented them with gold and silk upon their return to their homeland....
Professor Jeong noted the historic irony that Islam was brought to Korea on the (horse)back of non-believers. This irony could be taken even further by noting that the afore mentioned non-believers were not just your garden-variety infidels, but the very same enemies of God who that year had single-handedly stuck a fork in the Islamic Golden Age with the “Mother of All Sackings” of Baghdad.
Following the Mongol conquest of Goryeo, the saengmokin, regarded by the Mongols as highly cultured and educated (many Central Asians, particularly Uighurs, served as administrators for the empire — even the Mongol script was invented by a Uighur), came to Korea as guards, military aide-de-camps and attendants to the Mongol princesses sent to Korea to marry the Goryeo princes. At the same time, many Muslims came to Korea in a civilian capacity as traders, with many settling down for good.
This paper explores the history of Islam in Korea from its first introduction on the peninsula in as early as 11th-century to the present day. Although Korea is rightfully perceived as a country whose religious landscape has been traditionally dominated by Buddhist temples, Confucian study halls, and shrines for Korea’s own folk religion, Islam has also secured a foothold in this East Asian country. The author reveals the traces of the early contacts with the Muslim civilization in Korea’s own culture, ranging from the adoption of advanced calendrical techniques to the import of a sophisticated distillation technology that came to be used for the production of soju, Korean rice wine. Against the backdrop of this historical overview, the paper goes further to analyze why Islam has not made more headway in Korea. This research concludes suggesting that Islam’s failure to adapt itself to local customs accounts for its status as a minority religion that attracts primarily foreign residents of Korea and has only a small number of Korean adherents.