A reliable global total seems impossible: we know too little of slave numbers outside the areas of European control. For the 1780s as the trade was nearing its peak, Klein gives rather over 3 million in the Americas: 1.5 million in Brazil, 660,000 in the French Caribbean, 575,000 in North America, 380,000 in the British Caribbean and 100,000 in Peru & Mexico (Herbert S Klein, African Slavery in Latin America and the Caribbean). Numbers paradoxically rose as the Atlantic trade declined and neared extinction: US slave numbers approached four million by 1860, while Brazil may have peaked at around two million, and British numbers reached 700,000 before emancipation. Servitude survived in various forms on other continents, involving millions in Africa alone into the 19th century and even beyond: numbers are largely conjectural and there are issues of definition and political manipulation, but a global total of 20-30 million in various forms of bound labour doesn't seem implausible.