The Reborn General's Revenge

In his past life, the protagonist defended the Northern Border, but was betrayed by an Imperial Court inspector who colluded with the enemy, leading to his army's annihilation and his death. Reborn, he returns to the eve of the great battle, holding evidence of the treason. He exposes the inspector's conspiracy and executes him, purging the traitor to lead the border army and defend the northern gate.