I wouldn't use today's bumbling and inexact terms for that time in our history.
--- "And what sort of people live in these Northern Republican strongholds now?"
What "Northern Republican strongholds?"
I think you don't want to answer the question because you know what the answer is and you don't like it.
What "Northern Republican strongholds?"
Boston. Chicago. Baltimore. New York. You know, the places where Republicans were strong in 1860.
What are those places like now?