Despite his Congregationalist upbringing, Lewis Tappan became attracted to Unitarianism for intellectual and social reasons. William Ellery Channing, a Unitarian minister, became Tappan's pastor. As a peace advocate, Channing played an influential role in Tappan's decision to join the Massachusetts Peace Society. In 1827 his brother Arthur convinced him to return to a Trinitarian denomination. Tappan joined Arthur in the Congregational church. Lewis Tappan initially supported the American Colonization Society (ACS), which promoted sending freed blacks from the United States to Africa, based on the assumption that this was their homeland, regardless of where they were born.