C. The process of evolution
The main reason why the border states did not secede in 1860-1862 was because they were concerned with the large amount of military coercion that was taking place in the South, and they felt that the South was ultimately unjustified in removing itself from the Union.
Lincoln said this because his ultimate goal was to preserve the Union. Although he detested slavery on moral and economic grounds, he thought that it would eventually die out on its own, if it could be contained where it was.
