In 1929, the Board of the seminary reorganized along more liberal lines, and began hiring professors who were significantly more friendly towards modernism and some forms of liberalism.
Machen and a group of other conservatives objected to these changes, forming Westminster Theological Seminary in 1929. Then, objecting to theological positions that he believed compromised the distinctives of the Reformed tradition, if not the basic tenets of Christianity itself, Machen pled his case before the General Assembly of the PCUSA. The Assembly refused to take action, and so Machen and several other professors, along with a group of fellow conservatives, formed the Independent Board for Presbyterian Foreign Missions.
In 1934, the General Assembly condemned this action and Machen and his allies were relieved of their positions and effectively thrown out of the denomination.