Of course, the missionaries came soon after the true Faith took root. And, for the Faith to grow, the blood of martyrs provided the nourishment.
Sometime in the mid-eighteenth century, Korean ambassadors working in China came across Catholic books in Beijing that the Jesuits had distributed there going back to the mission days of Matteo Ricci (1597-1610). The ambassadors were of the noble class, well-educated, and considered to be sages by their people. The predominant religion in Korea at that time, at least among the upper class, was Confucianism. These sages brought the Catholic books back to Korea, studied them, shared them with the educated class, but did not convert at that time because they were waiting for the leaders of the nation to do so first. One of them, however, Ni-seung-houn, decided to go to Beijing in 1784 to study Catholicism. While in Beijing he was baptized Peter Ri. He returned to Korea and won many converts. Then began the one hundred years of persecution that produced 10,000 martyrs. Many of Peter Ri’s converts, among whom were Church leaders Paul Yun Ji-Chung and Jacques Kuen, and 123 of their companions, were martyred in 1791.
The first missionary to Korea was a Chinaman, Father James Tsiou. When he came to Korea in 1794, he found 4000 baptized Catholics. That is astounding, is it not? One man, Peter Ri, a layman, was responsible for that many converts. Father James Tsiou remained in Korea, building the Body of Christ sacramentally, until 1801 when he was arrested and martyred. The persecution did not diminish, it grew worse. The torments these 10,000 Catholics endured were among the most gruesome recorded in the Acts of the Martyrs.
Around the 1830s, a letter, pleading for help and missionaries, was smuggled out of Korea and carried to Rome. Pope Leo XII responded by sending missionaries and establishing an Apostolic Prefecture for the mission land. In 1836, Monsignor Lawrence Imbert managed to enter Korea. Others arrived, and they worked until 1839 when a full scale persecution was launched by the pagan authorities. The European priests were martyred. Native Korean seminarians had to get out of the country and they went to Macau to be ordained. The first Korean priest was Andrew Kim Taegon. He was slain for Christ in 1846. The blood of the martyrs was the seed of the Church in Korea as it was in the early Church. In 1864, an even more severe persecution began taking the lives of two bishops, six French missionaries, another Korean priest, and eight thousand Korean Catholics. In 1984 Pope John Paul II canonized en masse 103 of these martyrs, whose accounts were more popularly known. The Pope, himself, at the canonization ceremony gave the figure of 10,000 martyrs from the period between 1791 to 1866. Incredible as it may seem, Korea has the fourth largest number of canonized saints among all the nations of the world. Almost all of them are martyrs.
Here is a farewell letter written by Korea’s first priest, Father Kim Taegon, which he wrote for his parishioners while awaiting martyrdom along with twenty others. It was found among the manuscripts of French Bishop Antoine Daveluy, also martyred in Korea.
My dear brothers and sisters, know this: Our Lord Jesus Christ upon descending into the world took innumerable pains upon and constituted the holy Church through his own passion and increases it through the passion of its faithful….Now, however, some fifty or sixty years since the holy Church entered into our Korea, the faithful suffer persecutions again. Even today persecution rages, so that many of our friends of the same faith, among whom I am myself, have been thrown into prison….Since we have formed one body, how can we not be saddened in our innermost hearts? How can we not experience the pain of separation in our human faculties?
However, as Scripture says, God cares for the least hair of our heads, and indeed he cares with his omniscience; therefore, how can persecution be considered as anything other than the command of God, or his prize, or precisely his punishment?…We are twenty here, and thanks be to God all are still well. If anyone is killed, I beg you not to forget his family. I have many more things to say, but how can I express them with pen and paper? I make an end to this letter. Since we are now close to the struggle, I pray you to walk in faith, so that when you have finally entered into Heaven, we may greet one another. I leave you my kiss of love.
A list of the 103 canonized Korean martyrs, along with an abbreviated history of the founding of the Church in Korea (from which I obtained the above information) can be found here on CatholicOnline website.
Today the Catholic Church in South Korea is growing at an astounding rate. In 1960, Catholics made up less than 2% of the population of 23 million. From then to 2011 the population increased to 48 million, of which 10-11% are now Catholic.