The turning point came in 1758. The Philadelphia Yearly Meeting [of Quakers] recorded a "unanimous concern" against "the practice of importing, buying, selling, or keeping slaves for term of life." This was the first success for the cause of abolition anywhere in the Western world. "The history of the early abolitionist movement," writes historian Arthur Zilversmit, "is essentially the record of Quaker antislavery activities."
Quakers also took an active interest in the welfare of former slaves. Many masters helped to support their slaves after manumitting them. Others compensated them for their labor during slavery. When Abner Woolman (the brother of John Woodman) in 1767 freed two slaves his wife had inherited, he decided to pay them a sum equal to the amount that the estate had been increased by their labor, and asked the Haddonfield (New Jersey) meeting to help him compute a just sum.
This is from David Hackett Fischer, Albion's Seed: Four British Folkways in America, p. 602. I'm reading excerpts from Fischer's book for a forthcoming Liberty Fund colloquium on "Liberty and Diversity in the United States."
I had known that the Quakers were key in the abolitionist movement in the United States. I hadn't realized how key.
What's interesting also is that they, not surprisingly given their anti-slavery views, seemed to be the most libertarian group in the 18th century in what was to become the United States. This showed in their views on religious freedom. Many groups in the United States wanted the "freedom" to practice their own religion but not the freedom for others. But here's another quote from Fischer:
The most important of these differences [that Quakers had with other groups in British North America] had to do with religious freedom--"liberty of conscience," William Penn called it. This was not the conventional Protestant idea of liberty to do only that which is right. The Quakers believed. that liberty of conscience extended even to ideas that they believed to be wrong. Their idea of "soul freedom" protected every Christian conscience. (p. 597)
It's interesting to see how hard it was, though, even for such freedom-oriented people as the Quakers, to be completely tolerant of others' peaceful differences. Check this quote from Fischer:
Many Quaker immigrants to Pennsylvania had experienced this religious persecution; they shared a determination to prevent its growth in their own province. The first fundamental law passed in Pennsylvania guaranteed liberty of conscience for all who believed in "one Almighty God," and established complete freedom of worship. It also provided penalties for those who "derided the religion of others." (p. 599)