The Farsala Trilogy, by Hilari Bell, is about, well, rebellion, pretty much.
It centers around three characters: Kavi, Soraya, and Jiaan. The first book centers around Farsala's defeat at the hands of the Hrum and how the Deghans, the ruling class of Farsala, were all but wiped out. The second and third books center more on the seige of Mazad, the last 'free' city in Farsala.
Essentially, the Hrum have a law where if they fail to capture all of a country's strongholds within a year, then they will pull out and never invade that country again. So, basically, the Farsala Trilogy is about how the remaining rebels hold against the Hrum at the city of Mazad.
Regarding the characters: Kavi is a peasant peddler, Soraya is the daughter of the commander of Farsala's military, and Jiaan is her halfbrother through a peasant woman, so he is technically an illegitimate child.