The occupation left empty castles in its wake. Whole families were butchered in the initial invasion, and all those who couldn't or wouldn't bend knee to the Emperor's puppet king were declared traitors and hunted. Many bloodlines ended on Chevaliers' blades at dusty crossroads, in forest clearings, or in freeholds.
And then there were the turncoats.
To curry favor with their new masters, some nobles took up arms against their brothers. They betrayed and murdered the Rebel Queen, an act that created even more vacant titles and lands, once King Maric exacted justice.
That Ferelden did not fall apart after the Orlesians left is a testament to the strength of King Maric. The old families still held grudges against those who had sided with the emperor, and those new families that had been granted titles were viewed as interlopers. The Landsmeets that followed Maric's coronation were tense, to say the least.
--From Ferelden: Folklore and History, by Sister Petrine, Chantry scholar