Not sure what the plural for chlorapleth is (nice word! thanks for the education!)
Ximax: even if you doubled the population, traditionally you can only count on 5 to 10% of the population to fight (another 20% maybe in untrained militia - i.e., every abled bodied male of age), so you have only added 2000 soldiers tops, which is a drop in the bucket so far as controlling the province goes. Great empires usually have something else holding them together other than brute force - e.g., the Holy Roman Empire had a common heritage and church, while others had roads and mercantile infrastructure. Yet others have had cultural sway. Anyhow, most of the soldiers are likely from the country in any case, since there is where most of the population can be found.
My guess is that the combination of awe inspiring pyrotechnical illusions combined with a fair amount of genuine magical power for the hordes who remain unimpressed coupled with a really first rate diplomatic corp that keeps the various factions balanced against each other... most the last really! A natural reason for Ximax having the leadership role in the province can be summed up in "who else could do it?" I can well imagine the South Coast (probably the most powerful region) and the North Lake districts never accepting the other as sovereign over them. Add the nomadic central tribes with as a third, and there is no way they would be willing to bow to one of the other. But a little scholarly town out on the peninsula, with just enough force and power to be impressive, and quite defensible itself as history showed, but of a culture and kind quite different, one who was also not bent on micromanaging the different peoples, but primarily interested in preventing large scale war and maintaining general order throughout the province... All the different peoples of the province might very willingly bow to them as a first amongst equals.
Sometimes it is the small and the passive that can have the most authority and control. Just my two silver pennies.
May the ever evolving dream shower love, riches and joy upon you this Xmas.
Ringan