...The reason was a campaign by British Christian humanists. They had organised protests, they had won over MPs, they had won victories on regulating the conditions of slave ships, and they had published slave diaries and won court cases and shocked the country with tales of the atrocities committed in their name. Moreover they took advantage of the hatred of press gangs and the fear of sailing to make much of the huge death toll of the white crew on slaving ships who were dying to African diseases, this trade, they said, kills both white man and black and the message was heard. Throughout the 1790s there was a growing boycott of sugar by the abolitionists and non-voters signed petitions and sent letters to the parliament in numbers previously unforeseen. The result was a vote in the British House of Commons on abolishing the trade in slaves.
And they lost. 163 votes against abolishment to 88 votes in favour. In the aftermath abolitionists, on wondering why they had lost, blamed the timing. This was 1791. The Dolben Act, which had restricted the amount of slaves any one ship could carry had been passed in 1788. This was seen as the time for the abolitionists to strike, while the iron was hot. They had attempted to put up a bill in the same year on complete abolition of the slave trade but first William Wilberforce, their chosen politician, got sick before he could table the bill and when he recovered, King George had a fit of madness and so all other business was delayed a year while the discussion of the regency dominated parliament. In 1789 the pro slavery lobby delayed it further asking for time to find evidence to counter the claims about the slave trade and calling for further investigation.
The 1791 vote happened only after three years of delay, which the abolitionists deemed crucial to their defeat. Because during these three years a lot had changed. For a start the French revolution had happened and thus poisoned a lot of ideas of liberal reform in the minds of the British. Secondly the West India Lobby of pro slavery interests, who were barely existent as a united force in 1788, had begun to properly organise, the money they spent in lobbying increased hugely in each of those intervening years. Some of that money was spent on a PR campaign to rename the slaves 'assistant planters' in a reminder that satire often has a hard time outdoing reality. On the other side, the Abolitionist forces were weaker because James Ramsey, probably the most vigorous of all their campaigners, died in 1789.
One other thing had happened between 1788 and 1791, the first of what would become a series of slave revolts had occurred in the Caribbean which had been blamed on the abolitionists. This would set the pattern for the 1790s as the British would be faced with revolts in Jamaica, Grenada and Dominica. The French, newly destabilised by events at home, would fare even worse. A few months after the 1791 vote, a slave revolt in Haiti broke out, the largest the world would ever see. In 1793 the French, unable to defeat the slaves, instead agreed to free them, in 1794 this became a complete announcement across the entire empire that all slaves were to be freed and made full citizens. In practice the French Republic had limited power over a lot of their empire and a lot of colonies did not enact this law but this was still a hugely radical step...