The Tide of the Blood War Turns

In evil places the Blood War raged throughout most of history. Baatezu and Tanar’ri (devils and demons) fought eternally. Millions of demons were slaughtered as they were flung at the Baatezu war machine. Asmodeus had bigger ambitions than merely winning ground in a war, of course. He located a power. A terrible ancient power in the Abyss that enabled him to achieve Godhood. But the Baatezu war effort was powered by souls, and a huge influx of them was necessary to push into the Abyss. Thus, Asmodeus came to Atlea, twisting the entire Empire of Bael Turath to his whims. He tempted them all, promising them power in exchange for their very souls. It was not long before the Empire itself was comprised entirely of Tieflings, half-devil, half-humans. But it was still not enough. More souls were needed. Thus Asmodeus set into motion the events that would lead to the war between the dragonborn Arkhosians and the Turathi. The war fed souls to Asmodeus’ stores, giving him the extra he needed to push into the Abyss with an army. They did not last long, of course, but that was not his goal. His goal was to claim the ancient power, even if it meant sacrificing a lot of his soldiers.
He obtained the power, attaining Godhood for himself, while his soldiers in the Abyss were quickly overwhelmed by the sheer Tanar’ri numbers.
The Blood War did not last much longer. With his newfound power, Asmodeus brought the war to a complete stalemate. He retreated back to Baator, the Nine Hells to avoid open conflict with the gods for his heresy (this was, after all, the legacy of his betrayal of Io).
Meanwhile, the Arkhosian-Turathi war devastated their empires. Dragonborn and tiefling numbers dwindled to a handful.

The Tide of the Blood War Turns

Atlea and Beyond Stackle