The Splitting of the world

The splitting of the world was an event where the chaos god Zeraxi orchestrated a grand invasion of the brass realms in order to free its sibling the unceasing striving. While unsuccessful, the resulting conflict lead to a large-scale restructuring of the Brass Realms.

Prelude

When the Three Kings forged the Brass realms out of the fragments of reality remaining from the World-That-Was, they built reality from all aspects that were trapped inside the shell they built.
Any and all greater beings trapped within were integrated or otherwise rendered harmless, and their aspects made into part of the order. The Divine Machine was built and with it reality was perfect for a time. Everything was perfectly ordered and efficient, no molecule out of position and no energy wasted. In order to protect this perfect order, the three kings bound themselves in great chains so that their differences would not lead to the destruction of their mutual project.

However, unknown to them they had made a grave mistake. One of the beings trapped as reality was made was the unceasing striving, which was integrated and made into Vulcan. However its sibling, Zeraxi, was left outside the realms and it was enraged and bestowed with a unified purpose never before seen.
Zeraxi then, through means of persuasion, deception and guile, convinced others from beyond the brass realms to invade the Brass Realms. Its co-conspirators included Bliss, Delirium and many others.

The Invasion

Together the newly formed pantheon of chaos broke through the barrier surrounding the Brass Realms and started causing havoc. They began sabotaging the Divine Machine and broke multiple greater beings out of integration; Nindros, Gaia, The Nightmare King and many others were turned from purposeful and vital cornerstones of reality into actively dangerous rogue elements, ripping holes into the fabric of reality.

The Restructuring

The ongoing catastrophic damage to reality was threatening to break the three kings out of their chains. Should this come to pass, the resulting war between the gods of order and chaos would destroy the Brass Realms and return reality to the primordial chaos.
In order to prevent this, the Fateweavers and Mechanoids took drastic measures; They developed and deployed terrible weapons to fight the chaos gods and rampaging elder beings, to delay them and give time for the great machine to reorder reality from the perfection it was before to something more crude but all-together more robust.
After a great deal of fighting it was done and the divine machine split the world into three aspects, the material world, The Divine Machine and The Spirit World, three worlds where once there was one, all influencing one-another and all designed to resist intrusion.

The war and following restructuring of reality killed the native inhabitants of the Brass Realms; the Firstborn, and their souls and bodies were used as raw materials from which Worlds and the Living Stars were forged. This enraged Gaia and turned her into an eternal enemy of the mechanoids.

The New Order

In the aftermath of the Splitting of the worlds, a new order has crystallized. The chaos gods have successfully invaded the Brass Realms and have changed it forever, but they have not broken it. The Three kings remain in their voluntary imprisonment and the influence of chaos is constrained by The Dance of the Worlds.
Living beings in the Brass realms now are born in the material world, lead difficult lives filled with new concepts such as "pain" and "excess" and eventually pass into the spirit world to join in the great working by serving one of its many administrators. So the Brass Realms continue onward into the future.