Unnatural Immortal

In 1865 the Confederate States of America won the civil war. They won because they had a supernatural ally in a vampire named Argos and his undead slave army. Today more than hundred and fifty years later Amy Selkirk, driven by avenging the transformation of her sister into one of the undead, leads a rebellion to not only destroy Argos but to end the Confederate States of America, and thus end slavery, forever.
But she needs an allies, those willing to follow her example. A dark alternate history where good struggles to triumph over evil to save humanity.