Final answer:
The statement that 90% of slaves lived in the South in 1787 is true, reflecting the geographic concentration of slavery in the Southern United States due to agricultural demands.
Step-by-step explanation:
The statement that 90% of slaves lived in the South in 1787 is true. At that time, slavery was indeed a national institution, but it was significantly more prevalent in the Southern states due to the agricultural demands of crops like tobacco and rice. By 1790, the majority of slaves, numbering over 650,000, resided in the Southern states such as Virginia, North Carolina, South Carolina, Georgia, and the Southwest Territory, which later became Tennessee.
It is important to understand the demographic distribution of enslaved people during this period to grasp the social and economic fabric of early America.