Lincoln favored freeing black slaves
by deportation. He did not see blacks equals to whites. He used the slave issue only after 2 years of losing to the South.to stop the slaves s from helping the south and to gain the slaves help for the North.
Sout Carolina threatened secession in 1776
And slavery still is legal under the punishment Clause of the Thirteenth Amendment.
There were also four slave states that did not secede from the union Maryland being one of those. Robert E Lee's army of the Northern Virginia was attempting to go north to Maryland and get support of the slavers in Maryland to join his army and encircle Washington by controlling Maryland and Virginia but didn't work.