The Desert Spear by Peter V. Brett

In a world plagued by nightmarish demons, two men emerge as pivotal figures in the battle for humanity's survival. One, a charismatic leader from the desert, wields a powerful weapon and unites his people under a banner of war, while the other, a reluctant hero from the north, struggles with his destiny and the weight of expectations. As their paths converge, they must confront their own beliefs and the looming threat of the demon horde, navigating a complex web of alliances and enmities in a desperate bid to save their world from annihilation.