As the communists solidified their control of the North, it became increasingly difficult for evangelicals to live there. Consequently thousands of them fled to the South, constituting a significant portion of those who left the North between 1945 and 1953. Figures on the southward migrants are at best estimates, especially with respect to evangelicals. The number of all Koreans who migrated southward between 1945 and 1953 is estimated at between 1,014,000 and 1,386,000—about 10.7 to 14.7 percent of the average population (9,440,000) in northern Korea between 1946 and 1949. Kang Inch’ŏl estimates that in 1945 the number of northern Protestants was around 200,000, about 2.1 percent of the population. Of them, he estimates that 70,000 to 80,000 might have migrated to the South, constituting 35 to 40 percent of the Protestant population in the North and 6 to 7 percent of all northerners who migrated.
In the South, northern evangelical refugees became a force to reckon with. They zealously evangelized and built churches. In 1950 alone, they were responsible for 90 percent of the two thousand or so newly established churches in the South. Especially zealous were the Presbyterians. Their stronghold had always been in the North, in P’yŏngyang, but by the end of the Korean War a great many of them had migrated, constituting one of every four Presbyterians in the South. The northern Presbyterian refugees went on to build some of the largest and most influential churches in the country—including the Yŏngnak (Youngnak) Presbyterian Church (which in 1971 had a membership of twelve thousand, making it the largest Presbyterian church in the world) and the Ch’unghyŏn (Choonghyun) Presbyterian Church (one of whose elders. Kim Young Sam, became president of South Korea in 1992). From the 1950s to the 1970s, northerners led the church growth movement in the South, not only in the Presbyterian Church but in all the churches of evangelicalism.