Let us assume the following scenario happens that leads up to a total Bretonia collapse:
Bretonia and Kusari military forces at a stalemate
Both sides industrial capacity stimmied by resource limitations e.g. embargoes
With large manpower loses on both sides, the war falls into skirmishes
Gallia invades
Kusari surrenders and falls into a quasi-puppet state
Bretonia continues the fight, sadly due to lack of industrial might and manpower, slowly capitulates territory every year.
821 AS, Bretonia officially signs the Lewis Peace Treaty where it becomes a protectorate of Gallia in exchange for economic wealth. The Royal Family and military staff retreat to Liberty under asylum.
Gallia occupies Bretonian borders with Battleships and experimental carriers.
Liberty embargoes Kusari and Bretonia, resulting in a precarious economic position bordering collapse.
That is a rushed thought of things, but how would you see the workings of Sirius working with Bretonia and Kusari being knocked out as military powerhouses?
Personally? Gallia would make incursions into the Sigma's and Omega's for the resources for their immense war machine while the Bretonian and Kusari royal families would attempt to coax Liberty into a 'Liberation' role while Rheinland, seeing their options closing would attempt a peace treaty of necessity with Liberty.
Meanwhile, I can see the Nomads and The Wild building their forces while we destroy each other for a massive assault on the current forces. I mean come on!! The Nomads wanted us to kill each other militarily in the Nomad Wars, isn't that what is happening!?
but personally I'd say when Gallia reaches the lewis treaty,
they would have stretched their forces too far and the council would start backstabbing the navy in the core worlds of gallia,
so that would mean a joint RM/LIB force could knock Gallia out of Kusari or Bretonia,
as Gallia needs their fleets to preserve the crown's seat so said.
Another contributing factor....NPC rumors in Gallia, specifically the GMS base in Orleanais claim the king will be dead in a couple years from some mysterious terminal illness...