Rise of the fallen Wars of the realm series, book 2.

A six thousand year war rages and now the demonic Fallen are coming for him-the one man shrouded in mystery. Only Validus stands in their way. Validus is the last and least of God's angels, but he's seen much across the millennia since his creation. Empires have risen and fallen as angelic and demonic forces battle in a raging war that will determine humanity's fate-and the fate of his defeated brothers. Eventually called to be an earth-bound war...