Corean Chronicles, book 1: Legacies
L.E. Modesitt2002

In the barely recalled beginnings of recorded history, Corus enjoyed a golden age of civilization, its united peoples rich in learning, trade and the arts. A magical calamity spread a dark age across the planet, leaving its people to crawl slowly out of ignorance and savagery. Corea now stands a divided, warring world where kingdoms fight and people live amongst supernatural beings and bizarre animals. A few rare humans have Talent, the ability to use magical powers, and are thus either cursed or blessed. Alucius is one of the most Talented of all, yet came from unremarkable beginnings. Raised on an isolated ranch, he is warned never to show his Talent lest he attract attention and be condemned to a lifetime of service. He carries this warning as he comes of age, and joins the Militia as did his father before him. However, this is no routine rite of passage. Corus enters a time of flux as his country is invaded by slave armies of the immortal ruler Madrien - and Alucius himself is captured and enslaved. A palpable sense of evil hangs over the lands and those of Talent are the only defence.