Son of the black sword - Larry Correia

After the War of the Gods, the demons were cast out and fell to the world.Mankind was nearly eradicated by the seemingly unstoppable beasts, until thegods sent the great hero, Ramrowan, to save them. He united the tribes, gavethem magic, and drove the demons into the sea. Ever since the land has belongedto man and the oceans have remained an uncrossable hell, leaving the continentof Lok isolated. It was prophesized that someday the demons would return, andonly the descendants of Ramrowan would be able to defeat them. They became thefirst kings, and all men served those who were their only hope forsurvival.