Once again you don't even need nuclear war. Mass convict labor easily counts a slavery if the crimes the persons serving for are made up. Hell that actually happened in our timeline.
http://www.sahistory.org.za/article/history-prison-labour-south-africa
So really many of the people saying ASB are ignorant of OTL's history.
Using that logic the reintroduction of slavery in the United States is possible.