“Yet even amid the concert of the great powers [late 1814 in Vienna] there was evidence that it [progress] lived on as an ideal. That June, on his return from preparatory negotiations in Paris, the British Foreign Secretary had been greeted by his fellow parliamentarians with a standing ovation. Among the terms of the treaty agreed by Lord Castlereagh had been one particularly startling stipulation: that Britain and France would join in a campaign to abolish the slave trade. This, to Benjamin Lay, would have been fantastical, an impossible dream. The treaty, though, in the view of some in the British parliament, did not go nearly far enough. Castlereagh, anxious not to destabilize France’s recently restored monarchy, had agreed that French merchants should be permitted to continue trafficking slaves for a further five years. This, it had turned out, was a concession too far. Within days of the Foreign Secretary’s seemingly triumphant return from Paris, an unprecedented campaign of protest had swept Britain. Petitions on a scale never before witnessed had deluged parliament. A quarter of all those eligible to sign them had added their names. Never before had the mass of the British public committed themselves so manifestly to a single issue. It had become for them, the French Foreign Minister noted in mingled bemusement and disdain, ‘a passion carried to fanaticism, and one which the ministry is no longer at liberty to check’. Castlereagh, negotiating with his opposite numbers at Vienna, knew that his hands were tied. He had no option but to secure a treaty against the slave trade.”
Tom Holland Dominion: How the Christian Revolution Remade the World