Okay, first, this is not about the Alessian Empire, or the Reman Empire. They I(mostly) get. The Nords and Ayleids and gods and whatnot helped free the Cyrods and they became a nation of their own. And Reman ended up uniting a front against the Akavir and got the Dragonguard to help him establish his own Empire, which gave the Imperials a lot of Akaviri influence(that sort of disappeared in the games, it would seem).
I'm thinking more about the Septim Empire, where a warlord from Alcaire won the support to conquer Cyrodiil from the Nords and Emperor Zero and sets up shop in the White-Gold. At this point I would think that the Nords would get a lot of influence in the Empire, but this seems to be lacking. Then there is the Numundium stompy-time to make the Empire whole.
After that, it seems that the Cyrods as a race are the ones to largely take charge, and that is the part I start to wonder how that happened. I could have missed some hugely important piece of lore, but there seem to be a disconnect for me about this point. Is it just that Septim chose to adopt Cyrodilic culture, or just some freak accident?