The Age of Blood

From here is where the stories narrowed to what Avestrans knew. With Aeternum gone, the foundations of the realms had Avestra as their center. Those foundations gave birth to the realms and those realms gave birth to the Outsiders: a term for any race outside of Avestra.
Most of the Outsiders stayed to their realm but some of them had aspirations for more. They claimed they heard voices speaking to them. Many Celestials and Fiends believed the first aspects of the gods spoke to them. Others believed it was a calling from the Collapse that churned within Daestra.
What these beings were mattered little, what did matter was that these Outsiders were driven - no, compelled - to obey. Or that is one such story of how the Blood War began. What is known is the Celestials faced a massive invasion from the Fiends. Their homelands were tainted from the devastation and it seemed like the Celestials would fall.
That was until the Archdemons and Archdevils turned against each other. Their schemes could never allow them to work together permanently. And that greed, that disunity, is what inevitably destroyed their invasion. The Blood War turned from Celestial vs Fiend to Fiend vs Fiend. This led to what was seen as one of the most callous acts the Celestials took.
With divine magic, they cut off the Fiends from the Divine Realms with only one way to get back: One faction must control the homelands of all Fiends. And thus, the Fiends tear at each other’s throats across all realms except the Celestial realms… and Avestra.
Avestra, the supposed jewel of creation, was untouched by the ravages of cosmic war. Most believe it to be the gods while some believe it mortals or the Eternals themselves but a cosmic barrier protected Avestra and kept out the threats from beyond. And so the mortals of Avestra grew without fear from the stars above.