What did Lincoln mean when he said that "the nation will become all one thing or all the other"?

Question

A
Everyone in the nation will either move to the North or to the South.

B
Either everyone in the nation will become slaves, or everyone will become free.

C
All slaves will live either in the North or in the South.

D
Slavery will either become legal in both the North and South or be abolished in both the North and South.

Answer 1

B
Either everyone in the nation will become slaves, or everyone will become free.