Young Lord of Khadora by Richard S. Tuttle

A skilled warrior gets entangled in a corrupt political world, his cunning strategies pitted against thousands who seek his death. Marak challenges the clans of Khadora and the Chula, the dreaded cat people of ancient times, in a struggle that will change the fate of the world. Young Lord of Khadora is a tale of magic, military cunning, and political intrigue set in a land where honor is everything yet deceit is everywhere. From Goodreads.

In this world, when you lie you become the slave of whoever you lied to. This is what happened to Marek's mother. Everybody also has to swear vows of service to their lord. Son's of slaves can make the choice to become soldiers instead of being slaves and this is what Marek does.
At the beginning of the book Marek is promoted and purposely sent to failure. The problem is that he does not fail and he manages to communicate with the savages instead.
It ends a bit to neatly but it was still good.

This book qualifies for:
2015 Witches & Witchcraft Challenge
A Million More Pages Hogwarts: June Challenges
A Million More Pages Hogwarts: House Elves
A Million More Pages Hogwarts: Harry Potter: The Ultimate Series Tour
A Million More Pages Hogwarts: MARCHing Through Time
A Million More Pages Hogwarts: Diagon Alley Supply List
A Million More Pages Hogwarts: Backpacking Around The Globe
A Million More Pages Hogwarts: Hogwarts Scavenger Hunt