Before the eighteenth century, very few white men questioned the morality of slavery. The Quakers were among these few. The doctrines of their religion declared an issue such as slavery to be unjust. By 1775, the Quakers founded the first American anti-slavery group. Through the 1700s, Quakers led a strong-held prohibition against slavery. The Quakers’ fight inspired
growing numbers of abolitionists, and by the 1830’s abolitionism was in full force and became a major political issue in the United States.

The American Friends Society is still very much alive and involved in progressive and humanitarian work.

Here's a great blog that links to many other Quaker blogs.