J. Gresham Machen provided the fundamentalist movement with intellectual leadership by writing several important books including Christianity and Liberalism (1923), the thesis of which is that Christianity and liberalism are entirely different religions because of their different assumptions. He has striven to reform within the Presbyterian Church in the United States of America(PCUSA). He founded Westminster Theological Seminary in 1929 and formed the Independent Board for the Presbyterian Foreign Missions. He contended that the PCUSA had to be a confessional church and require its teaching officers to subscribe to the Westminster Standards. Carl McIntire was an admirer of Machen, and he joined the fight against liberalism. But they were driven from the PCUSA after their effort to reform the church over the issue of apostasy. They formed the Presbyterian Church of America(PCA). Yet within less than a year after the PCA was formed, in June of 1937, it was divided. There were the differences of opinion between Machen and McIntire during the period from early 1936 to January 1, 1937, when Machen died. And these differences primarily focused on the three distinct issues that represented also the differences between the majority and the minority of the PCA that would become later the Orthodox Presbyterian Church(OPC) and the Bible Presbyterian Church(BPC), respectively: dispensational ism, Christian liberty, and church polity. In other words, these differences were the reason for the division of the PCA and the BPC. . Machen represents the Old School element of doctrinal orthodoxy and lack of dynamic evangelistic thrust within conservative Presbyterianism in America. McIntire later began the Twentieth Century Reformation Movement. He represents the New School element of doctrinal latitude and evangelistic thrust in the heritage of Presbyterian fundamentalism. In terms of the doctrine of the church, while McIntire was a separatist, Machen did not hold to separatism. Also, Machen and McIntire exerted a great influence on the Korean Presbyterian Church especially through two great Korean theologians - Hyung Nong Park and Yune Sun Park. The Korean Presbyterian Church should pursue unity on the basis of doctrinal purity of the Reformed theology.