The first slaves in what would become the United States were brought to Jamestown tobacco plantations in the early 1600's, might be 1607, but I don't feel like googling it.
Anyway, anyone who has even the slightest doubt about whether the Civil War was about slavery needs a reality check. It wasn't about state rights, it was about slavery. The Confederacy thought Lincoln would abolish slavery, so they rebelled. In fact, its Vice President said "Its foundations are laid, its cornerstone rests, upon the great truth that the negro is not equal to the white man; that slavery . . . is his natural and normal condition."
To the north, however, it was about reuniting the country. Ending slavery became inevitable only as the war progressed, hence the 4(?) slave states that remained with the north.