Reborn as a Barbarian! Conquering Another World Starting from a Defeated Battle

Reborn into a low-tech barbarian tribe!?

In this story of rising to power, the protagonist is reincarnated as the chieftain of a defeated barbarian tribe, subjugated by a powerful empire. With their tribe on the verge of collapse after losing a war, the protagonist leads them in a fight to overthrow the empire and reclaim their freedom.