Underground Airlines is a 2016 novel by Ben Winters which is set in a contemporary alternate-history United States where the American Civil War never occurred because Abraham Lincoln was assassinated prior to his 1861 inauguration and a version of the Crittenden Compromise was adopted instead. As a result, slavery has remained legal in the "Hard Four" (a group of Southern states that have kept slavery): Alabama, Louisiana, Mississippi and a unified Carolina. Its name evokes the Underground Railroad in relations to its setting. The novel attracted praise for exploring racism through the alternate-history mechanism.