Fall of An Empire

A long time ago, Neveah tribe attacked their counterpart, the tribe of Heaven. It wasn't merely an attack to injure. It was an attempt of massacre. 

The historical records remain vague about the exact details but the outcome was crystal clear. It was a total victory for Neveah tribe. 

Sera tribe attempted a similar attack on Ares tribe and failed miserably. Not only did they not get their counterpart's sliver, they lost their own sliver.

Ativ and Vita fought but never at a full scale. It's as if they had an unsaid understanding that any victory in such situation would be phyric. And even the winners of the war would be baits to the other tribes. 

Against such a backdrop, the smooth victory of Neveah was particularly surprising. 

The scriptures of that period maintain that all tribes were roughly of equal strength, especially two counter tribes. Why then, did the war between Neveah and Heaven turn so one-sided?