about two thirds of them belonging to Protestant churches, and the rest to the Catholic Church. The number of Protestants has been stagnant throughout the 1990s and the 2000s, but increased to a peak level throughout the 2010s. Roman Catholics increased significantly between the 1980s and the 2000s, but declined throughout the 2010s. Christianity, unlike in other East Asian countries, found fertile ground in Korea in the 18th century, and by the end of the 18th century it persuaded a large part of the population, as the declining monarchy supported it and opened the country to widespread proselytism as part of a project of Westernization. The weakness of Korean Sindo, which – unlike Japanese Shinto and China's religious system – never developed into a national religion of high status, combined with the impoverished state of Korean Buddhism, (after 500 years of suppression at the hands of the Joseon state, by the 20th century it was virtually extinct) left a free hand to Christian churches. Christianity's similarity to native religious narratives has been studied as another factor that contributed to its success in the peninsula. The Japanese colonization of the first half of the 20th century further strengthened the identification of Christianity with Korean nationalism, as the Japanese coopted native Korean Sindo into the Nipponic Imperial Shinto that they tried to establish in the peninsula. Widespread Christianization of the Koreans took place during State Shinto, after its abolition, and then in the independent South Korea as the newly established military government supported Christianity and tried to utterly oust native Sindo. Among Christian denominations, Presbyterianism is the largest. About nine million people belong to one of the hundred different Presbyterian churches; the biggest ones are the HapDong Presbyterian Church, TongHap Presbyterian Church and the Koshin Presbyterian Church. South Korea is also the second-largest missionary-sending nation, after the United States. Buddhism was introduced to Korea in the 4th century. It soon became a dominant religion in the southeastern kingdom of Silla, the region that hitherto hosts the strongest concentration of Buddhists in South Korea. In the other states of the Three Kingdoms Period, Goguryeo and Baekje, it was made the state religion respectively in 372 and 528. It remained the state religion in Later Silla (North South States Period) and Goryeo. It was later suppressed throughout much of the subsequent history under the unified kingdom of Joseon (1392–1897), which officially adopted a strict