How and why did slavery become more prominent in the Chesapake?

Slavery in the Chesapeake region began in 1619, when a Dutch trading vessel carrying 20 African men entered Jamestown, Virginia. The slave trade expanded in the following years. Between 1700 and 1770, the region's slave population grew from 13,000 to 250,000. By the beginning of the Revolutionary War in 1775, Black people made up nearly one-third of the region's population.
In the 1800s, the Chesapeake region became a focal point of the national controversy surrounding slavery because it was in the unique position of spanning free, border and slave states:
“Free states,” which did not support slavery, made up the northern portion of the region.
“Slave states” encompassed the southern portion of the region.
“Border states” allowed slavery but were allied with the free states, further complicated the region's politics.

Ithink it's a, but i might be wrong