“On February 8, 1815, just days before his expected departure, Castlereagh could finally point to some success. France, Portugal, Spain, and others had come on board, and the Great Powers issued a joint declaration condemning the practice as “repugnant to the principles of humanity and universal morality.” They further agreed in the importance of putting an end to a scourge that had so long “desolated Africa, degraded Europe and afflicted humanity.” The slave trade should be abolished as soon as possible; France promised to do so in five years, Spain and Portugal agreed on eight years. Admittedly, this was slow and tentative, an abolition of neither slavery nor even of the trade itself. Yet it was a start, and human rights, for the first time, had been made a subject of a peace conference.
— Vienna, 1814: How the Conquerors of Napoleon Made Love, War, and Peace at the Congress of Vienna by David King
(The painting above is by François-Auguste Biard (1799–1882) and is entitled: The Slave Trade (Slaves on the West Coast of Africa) [La traite des esclaves] from circa 1833).