Part gathered from the walls in the ziggurat near Soro, written in a language that seems to combine both draconic and giant:

The world was created by the one god, he made 2 children. One to fly in the air with the wisdom of the skies, one to walk the land and the power to rule it.
The children were tasked to, together protect the world.
(note: combination of flighty and earthy music here)

After millennia, visitors came from another world (note: no mention of dimension, specifically “worlds”).

These visitors were small, far smaller than the children, and the came in many different guises. At first these visitors were looking for a safe place, which the children were happy to grant them. However the visitors had no respect for the one god, no even worse, they had brought their own heretical gods.

The children came together and decided that they would take these visitors under their wing (note1: we think that it was against the will of the visitors, note2 in some cases literally under their wing, note3: music picks up pace here).

The visitors bred quickly, quickly covering to much of the land. To reduce the pressure on the land and to appease the one god, the children began making sacrifices to the god.

Understandably the visitors did not like this for one bit and started to rebel, with the support of some of the children.

The conflict started to escalate, as at the same time the children noticed that offering the visitors gave them power. And some of them began offering, not for their god but to themselves. Centuries of fighting began, soon the conflict became one of retribution.
As the children began posing as gods themselves, their god left them.

From campfire tales of the hammers:

Stories were told of the different races from a different place than the old continent. A place that hey had fled, fled from some oppressors.

The halflings were the first to find a way to escape, and founded a new civilization on the “old continent” building ziggurats in their empire, mimicking the building style of their old masters. (note: some stories say fled, some say bought, some say selling out other races).

The dwarfs fled in underground passageways from a dragon as big as a mountain.

The dragonborn used to be slaves to these giant dragons.

The thieflings were the last to leave the continent, they blame the halflings for their long slavery.
(note, music from folk tales of every race while talking about the race)

From a vision of redemption:

Around the ziggurat near Soro, thousands of thiefling slaves, blood flowing down the steps in streams.

From the library found by Romero and Redemption:

From the old continent there has been an expedition before, they placed a town, called Dakaboh where now soro stands, this was 400 years ago.