Korea is the only region that self-proselytized to Christianity. In 1603, a Korean diplomat to China, Yi Gwang-jeong, met with a Jesuit missionary named Matteo Ricci in Beijing and became convinced of merits of Catholicism. When he returned to Korea, he began disseminating books given to him by the Jesuit and started the Catholic faith in Korea. In the late 1800s, when Korea was forcibly opened up to trade with West, Protestantism made its way to Korea.
Read more about Korean Christianity at this link: Wikipedia: Christianity in Korea