The slave trade arose as there was a shortage of man power in the United States as well as cost effectiveness.
The US settlers typically hired new settlers from the Old World in the beginning to work for them, but wages had to be fair and they were allowed to leave after a predetermined time period.
The US settlers then moved to using Native Americans to help work for them, but they developed little to no protection against European diseases, leading to a under population and a smaller work force to be used.
As the cotton & tobacco farms in the south required large amounts of work hands, the Americans turned towards using African slaves to help. With profits rolling in and greater production from having more hands on the deck, the United States continued to purchase slaves, primarily in the south. This led to what is known as a slave trade triangle, as the Americans bought slaves from Africa, in turn Africa received finished goods from Europe, and Europe received raw material from the Americas. With profit comes more investment into the venture, and with more investment means more people needed to work on the ever growing plantations to create more profit. This is what gave rise to the slave trade, the want for profit, and for money.
