according to wikipedia, there were only ~600,000 slaves ever brought to America. according to wikipedia, there were only ~600,000 slaves ever brought to America.Maybe to the US. But many were brought to the sugar plantations and mills of the Caribbean islands.
According to PBS, the loss rate across the Atlantic was about 10-20%, which sounds about right. So we're talking about around 100K deaths, not hundreds of millions.
Remember, the slaves were valuable cargo, and the captain would only be paid for the ones who arrived in acceptable condition, so the crew tried hard to keep them alive and healthy.