Meh, nationalism wasn't exactly a thing during these times anywhere barring Greece, Persia, and Egypt
Also, there is no direct control in the Mandala. It's still a confederation. The won lands were divided up into small Kingdoms given to cadet lines of the Dynasties of the Sen, Chand, Shakya and other dynasties of the Mandala; with them administrating from the regional capital. Really, the High King only really had full control over the military and foreign policy. As you can see in some chapters, administrative reform required the support of the Kings of the Mandala.
Though yes, you are correct; unrest will be there' heaps of it.