Thirty years before Lincoln issued the Emancipation Proclamation, the antislavery movement won its first victory in the British Parliament. On August 1, 1834, the Abolition of Slavery Bill took effect, ending colonial slavery throughout the British Empire. Over the next three decades, "August First Day," also known as "West India Day" and "Emancipation Day," became the most important annual celebration of emancipation among people of African descent...