The slaves were transported to the Americas for profit so the people involved in transporting the slaves, were only concerned in getting the job down with as many healthy slaves for as little cost as possible. There were many routes that the slave ships took. Over one route, ships from Europe transported manufactured goods to the west coast of Africa. There, the traders exchanged the goods for slaves. Next, the slaves were carried accross the Atlantic and to the West Indies for huge profits. This part of the passage is known today by most historians as the middle passage. The traders used the money that they got from the sale of the slaves to purchase raw materials such as sugar, coffee, and tobacco. The ships took these products back to Europe.
On the second triangular route, ships from the New England Colonies carried rum and other products to Africa, where they were exchanged for slaves. They then took these slaves to the West Indies to trade them for sugar and molasses. With this purchase, they took the sugar back to New England to be sold to the um producers.
The Atlantic slave trade operated from the 1500's to the mid-1800's. No one knows how many Africans were enslaved during this period. The most reliable sources tell us about 10 million blacks.