The Mourners: The Deadly Elite - The Mourners Series, #1

After the American Civil War ends in a stalemate, the southern states become a separate nation and their government is overthrown by Minister Samuel Davis, later known as the Apostate. Over a century later, his followers, the Apolites are thriving in the superstate of Scopus, a seemingly utopian society where a fundamentalist regime has kept their subordinate states in line and more importantly the people themselves, equal.
Once a year, all twenty-one-year-old Apolites must take an aptitude test to be assigned their life's work and consequently their place in society. Elide Hester, a mute, studious young woman living in dystopian Texas, who has spent all of her life preparing for the test, is relieved when she receives a high score. But when she is suddenly selected by a deadly pseudo-religious organization to be initiated into their ranks, she discovers that nothing is as it seems, including the country's enigmatic leader himself.
And with war threatening their borders, Elide must stay alive long enough to unravel the secrets of their past and master a power that could be the key to ending the war-or risk the destruction of everything she holds dear.