Midnight tides : a tale of the Malazan book of the fallen / Steven Erickson.

Enhanced descriptions from Syndetics:

After decades of internecine warfare, the tribes of the Tiste Edur have at last united under the Warlock King of the Hiroth, There is peace--but it has been exacted at a terrible price: a pact made with a hidden power whose motives are the best suspect, at worst, deadly.
To the south, the expansionist kingdom of Lether, eager to fulfill its long-prophesized renaissance as an Empire reborn, has enslved all its less-civilized neighbors with rapacious hunger. All, that is, save one--the Tiste Edur. And it must be only a matter of time before they too fall--either beneath the suffocating weight of gold, or by slaughter at the edge of a sword. Or so destiny has decreed.
Yet as the two sides gather for a pivotal treaty neither truly wants, ancient forces are awakening. For the impending struggle between these two peoples is but a pale reflection of a far more profound, primal battle--a confrontation with the still-raw wound of an old betrayal and the craving for revenge at its seething heart.