Thomas Clarkson. He, along with another Englishman, William Wilberforce, would lead this fight to end the trade.
Opposition to slavery existed from the outset among enlaved Africans themselves. Even among Europeans, occasional opposition went back much further than Clarkson's 1785 essay -- almost back to the beginning of New World slavery itself. In 1643, the New England Confederation assisted runaway servants, including slaves. In 1652, Rhode Island declared that a slave must be freed after ten years of service. In 1676, slavery was prohibited in West New Jersey. The Quakers were another outspoken group against slavery. Their writings had great impact on the opinions of both Americans and Europeans.
In England, a humanitarian milestone was reached in 1772 when the courts decided in the famous Somerset Case that a slave became free as soon as he set foot on English soil. Slavery was abolished within England, but it was still permissible within the colonies, as was the slave trade itself.
Eliminating England's involvement with the slave trade would be no small task. Directly and indirectly, the trade supported many of England's industries, including textiles, sugar refining, and the manufacture of firearms. In 1787, two years after writing his essay, Clarkson helped organize a group called the Society for the Abolition of the Slave Trade. The group wanted to make a case to Parliament, but first it needed evidence. So Clarkson travelled to Liverpool and Bristol, England's two major slave ports, to interview anyone with first-hand knowledge of the trade. With this ammunition, the group approached William Wilberforce, a Member of Parliament. He readily agreed to present their case. The fight for abolition of the trade was joined by many others, including former slave ship captain John Newton, former slave ship surgeon Alexander Falconbridge, and ex-slave Olaudah Equiano. They, along with countless others, began to sway the opinion of the public.In 1807, Parliament finally passed a bill that made it illegal for any English vessel to take part in the slave trade.