They do not, however, have any particular right to keep their regions.
Pardon my ignorance as I'm unclear on why this rule exists in the first place, but why does a region lord not have a right to his region?
He has more control over it than any other individual. It isn't a pie-in-the-sky title referring to an abstract concept like a realm. The Baron of Keplerville has a big estate in Keplerville and everybody in Keplerville knows him. If he says 'we are leaving this poop realm and joining this stronger realm right next door,' unless he is an absolute arse or has several knights who are not inclined to do the same thing, nobody in Keplerville is going to do much about it.
If Terran had four regions and two of them joined another realm, nobody would say anything. But when two of two regions join another realm it's a problem? What exactly is served by stopping this?
I'm not involved in any of this, I am just really surprised lately by how much effort you guys spend telling people that they can't do what they want to do when the only basis for a complaint about what's going on is a rule designed to stop big mergers rather than anyone actually able to demonstrate harm. I thought BM used to be all about hating rules lawyers.
