Excerpts from Books and Wikipedia
"Scattered attempts to prohibit slavery had appeared in the seventeenth century—notably in Rhode Island in 1652—and a protest was lodged in Pennsylvania in 1688. Few whites, however, showed much interest. Then, in 1754, John Woolman and Anthony Benezet, Quakers from New Jersey and Pennsylvania, published tracts condemning slavery. The Yearly Meeting of Pennsylvania, New Jersey, and Delaware Friends issued a formal declaration calling for its abolition: keeping slaves 'tends to harden the heart and render the soul less susceptible of that holy spirit of love, meekness, and charity, which is the peculiar character of a true Christian.'" [Toward Democracy, Kindle Location 6191]