Dunewarrior. Stormweaver, #5

The desert holds new dangers and the oasis cities are unprepared. Alissa and Reith struggle to find each other again in Pangaea's increasingly precarious situation on the brink of invasion. Stolen military secrets, disrupted route-finding, and ambitious warlords are converging to make the conclusion inevitable. They will be forced into open warfare before they have enough preparation to take on the heavily-armed invaders.
Dunewarrior is the fifth book in the Stormweaver series, the far-future fantasy epic from Jay Aspen.