But isn't Jenred interested in expanding his Empire?
Indeed he is. But he's firmly of the opinion that, say, thirty regions under leadership that is all competent is better than thirty five with incompetent leaders. It also makes good political sense, as the rest of the island will be far less likely to unite against the empire if they see that it only unites for good reasons and not just to save parts of itself. Now, given that this is
Jenred we're talking about (who is by far the most insane character I've ever roleplayed in or out of Battlemaster) "good" reasons may be a little flexible, but the Far East seems to have accepted that about him. Not even the Zonasans really protested when he marched an army down to sack half their realm over Erandi's (quite mild) insult to Edara.
From the Monarch level...Why would you want to help one of your rivals for rank keep power against you unless the emperor made an issue of it? Sure, there may be the usual politics and alliances, but everyone has to contend with those so that's not an empire-specific problem.
And even more importantly, from an OOC standpoint, that's just not fun. I'm somewhat skeptical about how often people claim gangbangs happen for no reason (as I've seen just how many times those protesting thought that insulting every other Ruler and pissing on their religion didn't justify the gangbang) but I'm fully aware that the phenomenon does happen, and want to prevent it as much as possible. Hence why I really like the challenge system. Bringing legitimate, guaranteed, almost whenever you want one-on-one wars with both sides barred from accepting any outside help and a set time limit so the war doesn't get old and boring? That's one of my dreams come true, and I think that holds for a lot of other people too.