From an email posted to Baen's Bar Honorverse dated October 21, 2004:

Why does Mesa still exist?

    Mesa is not alone. I don't want to go into too much detail, since this is something Eric and I are going to be developing in the CoS stories, but Mesa has been around for a long time and has made a lot of friends in its immediate area. Mesa was originally founded by renegade Beowulfans who disagreed with the Beowulf Code and who gradually worked their way from rejection of the Code into the active creation of genetic slavery. They (the ruling class of Mesa) have also been practicing genetic modification on themselves almost from the beginning. Anisimovna & Friends are the result of multi-generational improvement programs, and many of them (on a purely physical level) are at least as "advanced" as Honor herself, although I doubt many of them would want to meet either Honor or Thandi in a dark room. From the viewpoint of "natural" (as in, even without prolong) lifespan, physical health, resistance to disease, etc., etc., the Mesans are considerably superior (in the purely physical sense, at least) to "pure strain" humans. Because of this, they have a certain "master race" mentality. Genetic slaves are sub-human, in their view of the universe, pure-strain humans are merely-human, and they themselves are super-human. This is bad enough, but, aware of the need to protect themselves, they have made their services available to the populations and ruling elites of other SL planets in their vicinity. In short, there are quite a few (exact numbers deponent saith not) of "joined-at-the-hip" SL star systems in the area immediately around Mesa who see themselves as part of the "Mesan community," tend to follow the Mesan lead, and would use their veto in the SL legislature to stop any military movement against Mesa in a heartbeat.