For most of its history, the Atlantic slave trade faced little organized opposition in Europe. Then, in a few decades at the end of the eighteenth century, it became the target of one of the first modern mass movements. How did something so ordinary come to seem intolerable?
Quaker conscience
The first sustained opposition came from a small religious group. Quakers believed that every person carried an "inner light" from God, a belief that sat uneasily with owning people. Writers such as John Woolman and Anthony Benezet in Pennsylvania urged fellow believers to give up slaveholding. The Society of Friends, or Quakers, was the first group to organize against slaveholding by its own members. The Philadelphia Yearly Meeting moved to discipline members who bought or sold slaves in 1758 and later required them to free those they held. Because Quakers had networks of merchants and printers on both sides of the Atlantic, their ideas travelled fast.
The London committee
In Britain, the lawyer Granville Sharp had already fought cases on behalf of Black people in England, including the Somerset case of 1772. In 1785 a young Cambridge student, Thomas Clarkson, won a university essay prize on whether it was lawful to enslave people against their will; researching it changed his life. On 22 May 1787 twelve men met at a London printing shop and founded the Society for Effecting the Abolition of the Slave Trade. Nine of the twelve founders were Quakers. They chose to attack the trade first rather than slavery itself, believing it an easier target and hoping that ending supply would force planters to treat people better.
They recruited William Wilberforce, a member of Parliament who had undergone an evangelical conversion. In his first great speech in 1789 he said of the trade: "So enormous, so dreadful, so irremediable did its wickedness appear, that my own mind was completely made up for the abolition."
Gathering evidence
Clarkson rode thousands of miles collecting evidence. He interviewed sailors, copied ships' muster rolls and bought shackles, thumbscrews and the instruments used to force-feed captives. Clarkson's research showed that slave ships killed their own sailors at high rates, a finding that appealed to MPs who cared about the navy more than about Africans.
Black voices
Formerly enslaved Africans in Britain were central to the campaign. The Sons of Africa were a group of Black abolitionists in London who wrote letters to newspapers and to politicians. Among them were Olaudah Equiano and Ottobah Cugoano, whose book of 1787 demanded not only an end to the trade but the freeing of all enslaved people, a more radical position than the London committee's.
Mass politics
The campaign invented tools that activists still use. The potter Josiah Wedgwood produced a medallion showing a kneeling chained man. The Wedgwood medallion bore the words "Am I Not a Man and a Brother?" It was worn as jewelry and set into snuffboxes. Towns sent petitions: in 1787 more than 10,000 people in Manchester signed one, and in 1792 Parliament received over 500 petitions. Women, barred from voting, organized and joined boycotts. In the sugar boycott of 1791 to 1792, some 300,000 Britons refused to buy slave-grown sugar.
Defeat and victory
Success did not come quickly. In 1791 the Commons rejected Wilberforce's bill by 163 votes to 88. The great revolt in Saint-Domingue that year and war with revolutionary France from 1793 made reform look dangerous, and the movement stalled for a decade. It revived through clever tactics. The Foreign Slave Trade Act of 1806 banned British supply of captives to foreign colonies, presented as a wartime blow against France. Since it ended a large part of the British trade, the full ban was easier to pass. The Slave Trade Act received royal assent in March 1807. Britain was not first: Denmark and Norway, then one kingdom, issued the first national ban in 1792, to take effect in 1803. The United States banned imports from 1808.
Worked example: planning a campaign in 1788
Imagine you sit on the London committee in early 1788. Your goal is a vote in Parliament, but most MPs are tied to trade, and the public knows little about the ships. What do you do? First, evidence: you send Clarkson to Bristol and Liverpool to collect facts that are hard to deny, including sailors' deaths. Second, images: you print the plan of the Brookes and a medallion that asks a simple question. Third, numbers: you encourage towns to send petitions, so MPs can see that thousands of their constituents care. Fourth, allies: you give a platform to Africans who have lived the trade, whose testimony carries an authority no committee member has.
Notice the choices. Targeting the trade rather than slavery itself won wider support but delayed freedom for those already enslaved, a compromise Cugoano criticized. Appeals to sailors' lives and national interest worked on some MPs but put Africans' suffering second. Every campaign makes such trade-offs, and judging them fairly means asking what was possible at the time as well as what was right.