Final answer:
By 1775, African Americans were a significant portion of the 13 colonies' populations, with large concentrations in the South, especially South Carolina, and notable numbers in northern urban and agricultural areas. Approximately 350,000 blacks were enslaved across the colonies, revealing that slavery was a national, not just southern, institution.
Step-by-step explanation:
By 1775, the population of African Americans in the 13 colonies was sizable and varied greatly depending on the location. In regions such as South Carolina and Georgia, Africans were a substantial part of the population. For instance, Africans in South Carolina numbered 2,444, making up 75% of the total population around the opening of the eighteenth century and this demographic continued to grow. By 1740, they outnumbered Europeans 2:1.
In the North, slavery also existed, although it was more concentrated in cities and agricultural areas such as Rhode Island and Connecticut. By the 1770s, slaves made up 30 percent of the population of South Kingston and had significant numbers in cities like Boston and New London. Notably, many prominent New England merchants gained wealth through connections to the slave trade. In Georgia, despite declarative opposition to slavery, around 18,000 enslaved people were part of the population leading up to the Revolutionary War.
Overall, by 1760, it is estimated that somewhere around 350,000 blacks were enslaved in the American colonies, with Virginia and Maryland accounting for a substantial number, and significant populations in the northern colonies, like New York and New Jersey. Slavery was indeed a national institution, not limited to the South.