About 100 million in 1800s but that doesn’t account for population growth and devastation in 1600s, 1700s as well. My article discusses the breadth of death from in Africa to the ships to the numbers who died in slavery itself. Millions dying in battles plus on the trek plus in dungeons plus on ships plus in or as a result of slavery (including people born into slavery) isn’t hard to reach 30+ million in the span of slavery.