King's Legacy — R. Mac Wheeler

The king called him a visionary, named him his heir, but those who expected to rule threaten rebellion. If Justen avoids the assassins and civil war, he faces a looming destiny that will require remolding the world's beliefs, or clans will continue to perish. He's only beginning to discover his arcane power, what many consider taboo. Not wielding it, his success is less likely. Though he can't alienate those who would follow him.

The Clan Dyfyd series is set far in the future on a planet colonized millennia ago by humans determined to live without technology. Wars, plagues, the feudalism and customs they follow, drive them ever-faster to an unsustainable population.