The Faded Sun (C.J. Cherryh)

This is one story in three books: Kesrith, Shon'Jir, and Kuruth. The mri are a humanlike alien race who served as mercenaries to another race, the nearly sedentary Regul, in their decades-long war with humans. Now there is a treaty to end the war and form an alliance with the Regul, and the mri are seen by their erstwhile employers as a loose end that needs to be cut off. This complex tale (three books, after all) involves intrigue, misdirection, and the deaths of individuals, worlds, civilizations, and species. A human special forces man, brought in to serve as aide to the governor to one of the planets humans claimed in the peace settlement, and one of the last of the mri fighters become unlikely allies in the battle to save a people. The characters sometimes feel a little wooden, puppet-like to the plot, but the sprawling story and the depth of the plot made up for these weaknesses, and I hardly shouted at all to myself about the whole "desert planet" trope.