I'm pretty sure the answer is indigo. If I'm wrong then I apologize.
https://www.usatoday.com/story/news/nation-now/2018/02/08/column-why-america-cant-get-over-slavery-its-greatest-shame/1000524001/ check this site out it has some pretty good reasons you can use
Education or health services.
"popular sovereignty" which really just allowed settlers of the territory to decide whether slavery would be banned within their new state's border. Causing many people to rebel including the KKK.<span />