IME, republics and democracies prove to differ only in the titles they give the councilors.
When it comes to stability, the government style is irrelevant. All the treaties, constitutions, and all that other jazz aren't worth anything more than the paper they're written one. It's the attitude of the nobles in the realm that counts.
And that attitude is conditioned by government style. And I don't mean Theocracy, Tyranny, Democracy, Republic, or Monarchy on the realm info page. I mean how it really works within. Republics are oligarchic by definition. The power is concentrated in the hands of a handful of people who have been in the realm for a while, earned their power somehow, and have something to lose should the realm fail or take significant risks. Republicanism is therefore different than democracies, which try to be egalitarian, often by having everyone vote on a lot of stuff. However, people who have nothing to lose, like most knights, are much less risk-averse and therefore much more easily swayed by a good orator/propagandist, and therefore more likely to turn on allies as a good chunk of the voter base might not have ever dealt with said allies, and the alliance probably dates since before many of them were part of the realm. They are therefore more susceptible to drastic policy changes than republics are. Autocracies, on the other hand, offer a usually much more stable set of policy, but only for as long as you have the same ruler. If he gets replaced, everything can change.
Some "Republics" are much more democratic than most democracies.
Constant wars against your neighbors and multiple secessions does not strike me as "stable." I would call Riombara "highly volatile."
I would not. The wars have always been against the same people, secessions have been few and far apart, one of them resulting from a very particular context (invasion). Delvin has ruled until he got tired of it, and even with a series of newer rulers, Riombara is still doing the same old thing it always was.
Riombara is the epitome of stability, if you ask me. Nothing surprising ever comes from there. Same mentality and agenda since forever.
Stability has nothing to do with docility. A realm could be a stable warmonger, and another could be a peaceful realm of chaos. Stability is the consistency of realm politics over time. In a stable realms, rulers come and go (with the weeks or years, regardless), and nobody sees any difference for it in how the realm governs itself or deals with others.
