V.E Schwab 
Shades of Magic 
The Steel Prince #3.3

Led by the Antari magician Rowan, the Rebel Army’s wave of chaos has surged along the Blood Coast, decimating everything in its path. With each conquest, they offer a simple choice: join, and choose the path of power and freedom from a cold and distant crown, or die. With ranks bolstered by their conscripts, the Rebel Army mercilessly razed three cities, in a single night of terror and devastation. Now, a messenger has been sent ahead to Verose, promising the city that they too will be swept away by their might.Having failed to save the town of Milos, and the rest of the Blood Coast, Prince Maxim Maresh knows that this will be his last chance to quell the tide of the Rebel Army, or else risk the destruction of the entire Maresh Empire. But will the people of Verose stand with their Prince, or will Maxim and his Garrison have to face down Rowan and the Rebel Army alone?