Dread Empire's Fall: The Sundering

Description for DREAD EMPIRE'S FALL: THE SUNDERING by Walter Jon Williams:

The Dread Empire of the Shaa is no more, following the death of the last oppressor. But freedom remains elusive for the myriad sentient races enslaved for ten centuries, as an even greater terror arises. The Naxids--a powerful insectoid species themselves subjugated until the recent Shaa demise--plan to fill the vacuum with their own bloody domination, and have already won a shattering victory with superior force and unimaginable cruelty. But two heroes survived the carnage at Magaria: Lord Gareth Martinez and the fiery, mysterious gun pilot Lady Caroline Sula, whose courageous exploits are becoming legend in the new history of galactic civil war. Yet their cunning, skill, and bravery may be no match for the overwhelming enemy descending upon the loyalist stronghold of Zanshaa, as the horrific battle looms that will determine the structure of the universe--and who shall live to inhabit it--for millennia to come.

This is #2 in Dread Empire's Fall Series.