Okay, let us return to the original topic (or at least, the title of the thread).
I'ma gon' repeat my statement: It wasn't necessary so much as inevitable.
The Steiner-Davion civil war was a war without real 'fronts'-the supporters of each side (and the people trying-and-failing, to remain out of it) were scattered and interleavened among each other for the most part, with this being especially true in critical locations like Kathil.
BECAUSE of how the forces and sides were mixed in, the fighting on Kathil was simply inevitable, but the entire war was unnecessary. Victor had, before it even began, abandoned his role as Archon-Prince, and Katherine's secession (if examined truthfully) voided her own claim as well-at least, in any sort of legal sense. Unfortunately, Feudal systems don't rely on the law, they rely on personal fealty-Katherine built up quite a lot of influence and personal loyalties, enough to compromise significant portions of two nations simultaneously, while Victor absolutely abandoned his duty-so he could get laid.
Might be a great love story, but Victor's choice to give up his job for Omi basically put the whole nation into a leadership crisis, one that Katherine was all too well equipped to step into, but which she had no legitimate business stepping into.
the destruction and the grinding hell of Kathil as a front, was therefore both unnecessary, and inevitable.
Would that someone on the Fedsuns side, with Victor's abdication, have pointed out that they had a perfectly good candidate for First Prince, in the form of Peter-which would've been largely satisfactory under Fedsuns Law, given Peter had actually served at least PART of his required military time, was of the right bloodline, and was a direct and legitimate son of Hans-but there's no advantage for political operators in doing that and he was in the wrong half of the dual monarchy at the time and would have required someone to actually REMEMBER HE EXISTED.
(Eventually, someone did, and Morgan Kell recruited him to remove krazy auntie Nondi who'd been running the Lyran half into the ground on Katherine's behalf...but too late.)
This is the thing, though, isn't it? some of Hans's less brilliant traits included picking some pretty poor staff, due to his actually having the talent to be a bit of a micromanager (thus, depriving the realm of competent bureaucracy that could say 'Nah, princess, you're not legitimate' and make it stick.)
Kathil happened because the governments involved weren't...well...competent.
or at least, not competently composed, not competently led at the middle levels, and structurally very much in the mold of 'following orders even if they don't make sense'-and this goes for both the Kathrinist, and Victorist, factions-their loyalties were not to the nation, the realm or the law, but to personalities, and that ALWAYS ends badly in the final tally for the common people.