The Powder Mage Trilogy: Promise of Blood, The Crimson Campaign, The Autumn Republic

In a world where mages control gunpowder and bullets, a brilliant general must defend his country from both war and insurrection. Check out the complete Powder Mage Trilogy in this omnibus edition, a series that Brandon Sanderson called "Just plain awesome!"
In Promise of Blood: Field Marshal Tamas' coup against his king sent corrupt aristocrats to the guillotine and brought bread to the starving. But it also provoked war with the Nine Nations, internal attacks by royalist fanatics. Stretched to his limit, Tamas is relying heavily on his few remaining powder mages, including the embittered Taniel, a brilliant marksman who also happens to be his estranged son, and Adamat, a retired police inspector whose loyalty is being tested by blackmail.
In The Crimson Campaign: Drastically outnumbered and pursued by the enemy's best, Tamas must lead his men on a reckless march through northern Kez to safety, and back over the mountains so that he can defend his country from an angry god, Kresimir.
In The Autumn Republic: Field Marshal Tamas returns to his beloved country to find that for the first time in history, the capital city of Adro lies in the hands of a foreign invader. His son is missing, his allies are indistinguishable from his foes, and reinforcements are several weeks away.