The war they fought at the Praire River was only the beginning of a series of wars. After all, upon hearing the news of their defeat, the Yin Beasts and Nightmares from beyond the Empire poured into it.
Even though a lot had been killed, four Demons had survived, not to mention Su Daiyu and Su Zi. So, problems persisted continuously.
In the end, Krune had made a mistake, thinking that if he was too bloodthirsty, he wouldn't be a solution to the source of suffering in this world. Then again, none of the two was a solution, causing him to rack his brain, trying his best to do everything in his power.
With the Emperor dead, he had become the Emperor naturally, being a Star Imperial Meister and what not. So, he worked in bettering the living conditions of everyone, improving medicine, culture, art, etc.