Properly speaking, the early abolitionist movement dates from the late eighteenth century. But there were attacks on slavery and the slave trade before this period. Enlightenment figures, such as French philosophers Jean-Jacques Rousseau and Montesquieu, both expressed their disapproval of the Atlantic slave system, as did writers like Aphra Behn, the author of Oroonoko (1688), the story of an African enslaved in Suriname.
For the most part, these early critics focused on the inhumanity, cruelty, and immorality of the slave trade, themes that would be picked up by abolitionists in the 1780s. The case against colonial slavery was also greatly strengthened by political economists such as the Scottish Adam Smith, who argued that slave labor was costly and inefficient, certainly when compared to free wage labor. Others went further, condemning slavery on the grounds that it was harmful to personal industry, profitable economy, and family life. Slavery was increasingly viewed by many eighteenth-century Britons (and Americans, too) as part of a "system" that appeared outmoded and in urgent need of repair.
An important lead also came from the Religious Society of Friends, known as Quakers. Convinced of the utter sinfulness of physical coercion, American Quaker activists, following Anthony Benezet and John Woolman, succeeded in making abolition a test of religious truth. In 1758, the Philadelphia Yearly Meeting made involvement in the slave trade a disciplinary offence, leading to exclusion from all its business meetings.
Two years later Quakers in New England similarly changed their policy relating to slave merchants. Interestingly, there was an international or transatlantic dimension to this reform activity. In 1761 the London Yearly Meeting also announced that any of its members found guilty of involvement in the slave trade would merit disownment. Underpinned by an intricate web of family connections and business contacts, international Quakerism would prove to be one of the most dynamic and enduring factors in the campaign against both slavery and the slave trade.