The Dragon Republic (The Poppy War #2) - R. F. Kuang

Three times throughout its history, Nikan has fought for its survival in the bloody Poppy Wars. Though the third battle has just ended, shaman and warrior Rin cannot forget the atrocity she committed to save her people. Now she is on the run from her guilt, the opium addiction that holds her like a vice, and the murderous commands of the fiery Phoenix - the vengeful god who has blessed Rin with her fearsome power.