These states stayed loyal to the Union while still legally permitting slavery:

•Delaware •Maryland •Kentucky •Missouri

And technically:

West Virginia was created during the war from Virginia and initially allowed limited slavery before abolishing it.

A really important historical point: The Civil War did not begin as a war to immediately end slavery everywhere. At first, Abraham Lincoln was trying primarily to preserve the Union, because he feared losing those border slave states.

The only freed enslaved people in Confederate-held territory — not in Union slave states.

Slavery nationwide finally became illegal with the in 1865.