the Vilani seeded population wise much of the 15,000 planets of the first Imperium including all of Core Sector naturally as it was well within the borders of the First Imperium. 4000 years before any other race (the Zho's) even discovered jump technology they were at J-2. Sure they didn't progress much afterwards but... the inertial mass of that empire was mind boggling.
Absolutely right.
My big quibble has been the immense scope of the First Imperium is very apparent by looking at any map but its implications of that IMO haven't really tackled too well in canon...
Absolutely right. Excellent quibble.
Sorry but one world isn't taking out 15,000 not without a lot of the effort already having been done... ie the Vargr in the Coreward wars who had the technology that shear numbers that dwarfed Terra to grind down the First Imperium's huge numbers and fleets, which naturally would have taken all the attention and best forces the Vilani could muster due to the relative proximity to Vland sector and homeworld Vland, and leave Terra to fight the crumbs set against it. Sure the Terran Confederation is given credit by the historians (canon) for defeating the First Imperium, triggering its downfall but really is the best example of self serving history being written the 'victors'. Yet it was the Vargr who truly killed the First Imperium.
Counter-quibble:
The Terrans developed Jump 3 and meson guns before the Ziru Sirka or any other group. These Terran advances, severe political and social strife within the Ziru Sirka, and the general ineptitude of Vilani strategy and leadership is what killed the First Imperium.
The Terran Confederation had about 27 worlds by the later period of the Interstellar Wars. For many of the Interstellar Wars, it was Terra and its colonies against only the resources the Vilani provincial governor decided to deploy. What Terra considered 'wars', Vilani provincial governors considered 'engagements' or 'punitive expeditions'.
There was a civil war in the Ziru Sirka between the first and second wars with Terra.
Vilani fleets operating near Terra were at the end of their logistical chains.
Terran diseases devastated numerous Vilani worlds between the Third and Fourth wars between Terra and the Ziru Sirka.
The Vargr only became a problem on the Vilani coreward frontier after the seventh Terran-Vilani war.
The Vegans revolted against the Vilani, giving the Terrans a powerful stronghold in the rimward province.
Only after nine wars with Terra did the Vilani emperor send a massive fleet to crush Terra once and for all. This fleet, the bulk of Vilani fleet power, was destroyed by new Terran meson gun armed battleships. After this loss the Vilani were on the defensive until the Ziru Sirka fell.
the Villani probably should be the largest, by far, population segment of the Third Imperium.
I completely agree. I consider the Solomani to have been similar to the British in India or Africa. Many Solomani populations would've been completely assimilated by much larger Vilani populations during the Long Night, or remained distinct Solomani populations in instances where there was a viable Solomani population to sustain itself if it did not assimilate. Only in regions closer to Terra, where Vilani worlds were depopulated by Terran plagues, would there be majority Solomani populations or mixed Solomani-Vilani populations. By the time the Long Night ended, a "Solomani" in the former Imperial core would be a Vilani with a fraction of Solomani heritage, and would be unrecognizable to the Solomani of the Solomani Sphere.