Dawn Of Prophecy by Kenneth L. Powell

At the dawn of human civilization, beings from another planet land on Earth. At first, they seem friendly enough, promoting peace and sharing their incredible magic with the habitants of their new world.

While human in appearance, Dragonians have the ability to transform into the towering beasts we know today as dragons. Carving out a canyon, they create their capital and claim their own piece of land.

After a terrible tragedy during the birth of the Dragonian king's son, they begin enslaving humanity, imposing despotic rule over their new home. As the dragons' hold on the land surrounding their black castle begins to tighten, the king's allies begin to question his motive, and his sanity.

In the middle of a plot against the king and his rule is a young, untrained prince; a hero some don't believe exists. As he becomes more and more entwined with those plotting for change, he must open himself up to learn what he's missed his entire life.

Soon, he will learn what it truly means to be free, and what it means to fight for those who cannot.