You are aware that New Mexico became a state in 1912, aren't you? I don't think that slavery was much of a factor by then.
I know that. My information came from here. http://www.politifact.com/wisconsin/statements/2013/apr/21/paul-ryan/lincoln-backed-slavery-measures-us-rep-paul-ryan-s/
The area of a place did not necessarily mean statehood.