The Riven Shield (Mystic Seasons of Mythopoeia Book 1)

Mythopoeia rests in the boughs of a great ash tree that roots in darkness. Timothean was once a sorcerer, but gave up his humanity in a war against the gods in eons past. For thousands of years there has been order, a peace maintained by the magical artifice of long dead wizards. When Timothean decides to break that order, he must begin by shattering the defenses he helped put in place long ago

This is a tale of a world in the breaking. Only an immortal barbarian, a kobold raised as a pet by wizards, and a few young not yet heroes  stand between Timothean and the end of all things.