Gain a Friendly reputation with the Magram, then speak with Warug.
To beat the centaur, we must use their hatred against them. We will ally with one of the clans and through them, we will learn how to defeat all the clans.
If you choose to ally with the Magram then slay their foes, the Gelkis. This will earn you respect among the Magram. When you earn enough, then meet with the Magram spokesman Warug, on the outskirts of the Magram Village, in southeast Desolace.