Dread Nation by Justina Ireland

At once provocative, terrifying, and darkly subversive, Dread Nation is Justina Ireland's stunning vision of an America both foreign and familiar—a country on the brink, at the explosive crossroads where race, humanity, and survival meet.
Jane McKeene was born two days before the dead began to walk the battlefields of Gettysburg, Pennsylvania—derailing the War Between the States and changing the nation forever.
In this new America, safety for all depends on the work of a few, and laws like the Native and Negro Education Act require certain children attend combat schools to learn to put down the dead.
But there are also opportunities—and Jane is studying to become an Attendant, trained in both weaponry and etiquette to protect the well-to-do. It's a chance for a better life for Negro girls like Jane. After all, not even being the daughter of a wealthy white Southern woman could save her from society's expectations.
But...