It is my belief that the Sturgians are early Nords that traveled eastwards instead of southwards to Calradia. The real-world equivalent would make the concept of the Sturgians "russian vikings" or more commonly just called "The rus" (https://en.wikipedia.org/wiki/Rus%27_people).
I will theorize further that after the fall of the empire, the Battanians will have been vanquished and then immigrated into the Sturgian countryside, slowly over time having their bowman skills adapted into the Sturgian army and the Sturgians eventually become the Vaegir.
The Vaegir Guard and the Vaegir Marksmen represent both Sturgian and Battanian warriors respectively
I will theorize further that after the fall of the empire, the Battanians will have been vanquished and then immigrated into the Sturgian countryside, slowly over time having their bowman skills adapted into the Sturgian army and the Sturgians eventually become the Vaegir.
The Vaegir Guard and the Vaegir Marksmen represent both Sturgian and Battanian warriors respectively