As morally wrong as slavery was, the US owes alot to the slaves. Yes there were European indentured servants that worked on the plantations and the settlers actually preferred them over slaves. Usually the average life expectancy for slaves and indentured servants was about 4-6 years since they were worked so hard. And they figured if they were going to die anyways, they might as well use more indentured servants. This was because slaves were more expensive to buy from the slave traders. The slave trade was also just another enterprise for making money along with sugar, tobacco, indigo etc. Laws were also made to fine tune the institution of slavery to be more efficient. For example a new born was born into slavery if the father was a slave. etc.
For a long time, indentured servants were preferred. They were cheap, and there were a lot of them because England was going through tough times.
But Indentured servants eventually got set free, and had to go try their luck. Many did not succeed, and wound up landless, jobless, and restless. Oh, and they were armed and very annoyed with their lot. Suddenly, indentured servants were becoming a problem, because they were generating so much fear. They would attack and rebel often, and made landowners very nervous.
Meanwhile, england's economy improves. There aren't so many down-on-their-luck people in England. Hence, not so many people willing to be indentured servants. I mean, you had to be really desperate to go into indentured servitude.
And while all this is going on, slaves are slowly trickling into the colonies. Now, maybe indentured servants were cheaper, but you had to give them up after a certain period of time. And they were scaring a lot of people. So if you had the money, you might get a slave instead, because they were forced to work for you for life. And if your slaves had children, you got more slaves. In fact, many slaves were forced to have children, so that slave owners could get more workers for free. Because of this, slaves got cheaper. It was expensive to bring them over from Africa, but if they had been born in the colonies they could be sold for a lesser price.
The last thing that caused slavery to be popular was the beginning of rice as a cash crop. Rice wasn't like tobacco. It required a good deal of skill to grow. And many Africans possessed this skill, having grown rice as food in Africa. Indentured servants? Not usually so skillful. If you wanted to grow rice, you needed slaves. Huge numbers of slaves were captured for this very reason.