Conclusion
During the 1700s, slavery existed throughout the colonies (both north and south) that would ultimately become the United States of America.
To some colonists, including those in the north, the Trans-Atlantic slave trade was simply an issue of economics. The growing demand of labor resulted in the importation of over 250,000 enslaved Africans into North America to work on plantations and in homes. Most slaves in the north labored as farmhands, dockworkers, sailors, and house servants.
When the thirteen British colonies gained their independence and became the United States, the issue of slavery grew into a heated debate. Many northerners were against the institution of slavery. Many of the framers of the Constitution were against the slave trade, even though they owned slaves!
In 1808, as soon as Congress was permitted to ban the importation of the slaves (see the U.S. Constitution, Article I, Section 9), it did so; but slavery would continue to exist for another six decades.
Discuss: How can a "just" society exist if it supports the institution of slavery?
sources: Prentice Hall, U.S. History; Constitution Center; Slavery in the North.