Seriously, what are you talking about here? What atmoran army?
Atmoran
empire. The empire that conquered Tamriel? a better (correct) way to put it would prbably be the old Nord empire, before they were defeated/assimilated.
They were the first Nords (and humans) to land on the continent and conquered most of it before Nerevar and Kagrenac defeated them and they ended up another province of the Imperial Empire.
They are the same race, but they are a different people. The Atmorans of old aren't the same as the Nords.
I brought the Empire up because they are crumbling and will be defeated one way or another, when that happens the Imperials will be in the same state as the Nords are/were. Once great but now not so great.
I don't think you really get the difference in Nords and Atmorrans. They're basically one-in-the-same physiologically. Ysgramor wanted to be buried facing his homeland, but after that the Nords were Nords and Skyrim was their home. There's no "Atmorran Empire" that they pine for. There're even quips about how the Cyrodillian Empire is the Nord Empire! Tiber Septim was a nord and he started the Empire by taking his nord army and conquering Tamriel (with a little help from a weird robot, admittedly.)
The Cyrodillian Empire has forgotten its roots because Medes isn't of Nord blood. He's an Imperial. His concerns are understandably more aligned with where he was born and the people he consider his own. But that doesn't mean the Nords didn't start that Empire. It means that Empire forgot it.
They're probably going to be reminded in upcoming DLCs.
Tiber Septim may have been a Nord, but by the time of Uriel the Septims had mostly forgotten their own heritage identifying as Imperial politically rather than Nordic.
The Nords are the same race physiologically, they are not the same as when they first landed and conquered as Atmoran Nords in terms of power or influence. 500 Nords couldn't conquer the Thalmor for example despite being one and the same as the Atmoran Nords.
The Cyrodillic empire forgot it's heritage because the Septims either forgot it themselves or ignored it in order to rule impartially (read: for Imperial benefit).
Atmora was the continent the Nords originally hailed from, but never really a major army from it unless you count the 500.
Atmora itself was wiped out to an ice age to the last man (presumably, none alive have from to Tamriel since the seas froze)
It was also destroyed by internal politics that caused Ysgramor to leave forever, the Nords who landed to settle are what I am referring to as Atmorans.
You're kidding, right? The Dwemer were and are the most advanced race period. Did the Chimer win some battles? Surely. But they also had a patron deity in Azura the entire time.
Advanced scientific knowledge does not equal military strength. Although the Chimer mainly won above ground battles as far as I know, where they had the advantage.