As new magma cools and new rock is created the plates move farther and farther apart. But on the other end of the plate the plate subduction under the other plate making fresh magma and starting the cycle a new. The earth doesn’t increase in size due to the law of conservation of mass.
The south approved slavery because slaves were useful to them on their cotton farms. However, after the invention of cotton gin many saw that they didn’t need to slaves to work for them on the cotton fields anymore as it was easier to own a machine which would do the work instead. They saw the slaves as pointless and impractical after the invention.
René-Robert Cavelier, Sieur de La Salle
