Aftermath is a Star Wars franchise tie-in novel written by Chuck Wendig and published in September 2015 by Del Rey. Since Disney decided to declare all of the pre-2014 novelizations as a separate timeline from The Force Awakens movie in 2015, Aftermath is one of the few novels in the current movie timeline.
Aftermath picks up shortly after the original movie trilogy. The second Death Star has been destroyed. Darth Vader and Emperor Palpatine are dead. The Empire is shaken and leaderless, but not gone (keep in mind that this book was published before The Force Awakens hit theaters, so we hadn’t yet met Kylo Ren and the First Order yet). The Rebel Alliance has become the New Republic, trying to restore as much order as possible in the wake of the conflict with the Empire.