The Battle of the Gods (TBOTG)

When Atoz died or left, eight gods were left behind to rule over his creation. These beings were called The Eight Arms or The Arch Gods. They created lesser gods and the mortal races and were heavily involved with their lives. This is known as The Second Age. Historians are not in total agreement, but estimate this age to have spanned around 80.000 years. The Arch Gods instructed their worshipers (through divine visions etc.) how to build the portals, connecting the material plane to the godly domains. This made the gods able to travel effortlessly back and forth from the material plane.

A mortal started the war by killing a god and ascending to divinity. Another god is angered and fearful that other mortals might rebel, so he kills the new god. This divides the gods and races and a great war ensues.

The Alliances

Atozia was divided in three major alliances. One faction consisted of humans, elves, dwarves, halflings, gnomes and various other smaller races. Another consisted of orcs, goblins, tieflings, undead and other evil leaning races. The third alliance consisted mainly of dragons and dragonborn. When the last battle between the factions were to take place, most of the gods came to the material plane and joined the fight. This lead to the destruction of several cities and millions of casualties. The battle ended, when the gods saw the destruction and realized their wrongdoings. They made peace and their worshippers followed their example. This brought the realm into The Third Age.

Planar Gates

Atozia is connected to eight divine domains by ancient portals believed to be built by the Atozians - The Ancients. The gods used these portals to effortlessly enter The Material Plane to shape Atozia, and meddle with the lives of the mortals. This went on until The Battle of the Gods (TBOTG) where the portals were closed off, and the gods were banished to their respective domains. Rumors still speculate whether the gods are truly banished, or they still have ways to travel to Atozia. 

Countless lives were lost due to the battle and scholars estimates a third of the world's people perished. Much knowledge was lost as well. Technologies and magic the common people of the third age couldn't dream of were lost to be rediscovered.