In 1767 Gadsden's Wharf was constructed at the city port on the Cooper River; it ultimately extended 840 feet and was able to accommodate six ships at a time. Many slaves were sold from here. Devoted to plantation agriculture that depended on enslaved labor, South Carolina became a slave society: it had a black majority from the colonial period until after the Great Migration of the early 20th century, when many rural blacks moved to northern and midwestern industrial cities to escape Jim Crow.