Answer:
To exploit others in order to obtain profit..
Step-by-step explanation:
When you put other humans under slavery, you can force them to do anything you want without having to care about their rewards or general well being.
From colonial times to the civil wars, slavery were constantly used to obtain profit and reduce their expenditures.
The slaves were forced to work in extreme long hours without rewards by plantation owners in order increase their production. Even during the war, many slaves were used by the army to do dangerous jobs in order to cut down the casualties among their 'real' soldiers.