Slavery came to be the dominant labor system in the southern colonies because the colonies were predominantly agricultural and required vast amounts of cheap human labor to keep the cotton plantations running economically. Various economic and social conditions combined to make slavery a hugely effective and successful form of labor. Unlike earlier European and Native American slaves, the birth rate of African-Americans born to slavery outnumbered those dying, therefore negating the necessity to replenish numbers by buying more.
Paid slaves were also expensive and once new laws were introduced that indentured slaves to their owners for life, slavery formed a cheap, manageable, and self-replenishing labor force Slavery has been around in one form or another, for centuries. It’s natural that the affluent, white, land owners of the south would consider themselves superior to that of the poor, landless African-Americans. In the south, the physical differences of the first African-American slaves precluded them from running away and blending in with society like the European slaves had. Neither were they familiar enough with the land to escape as effectively as Native American slaves had. For the most part, African-American slaves had no choice but to submit to a life of slavery.
Slavery was economically viable due to a thriving slave trade, birth rates that exceeded mortality rates, and new laws that restricted the freedom of slaves. Combined with the white man’s sense of his own superiority, and the inability of African-American slaves to escape as effectively as European and Native American slaves, the social situation for African-American slaves encouraged the rise of slavery as an acceptable and sustainable labor source.