When I do a RPG a backstory as a DM I like to go back quite far:
Before time, there was oblivion, unmeasurable and without variance.
The endless nothing was so consistent that it had a pre-awareness of itself. Not a mind but basis for certainty, a confidence of how things were. That things could be different was impossible. That certainty revealed the notion of potential difference and then possibility came to exist; to have always existed. Possibility and difference resolved in multiple ways, this was the creation of the eight Fundaments: Connexion, Time, Thought, Life, Air, Earth, Fire and Water.
Time allowed a new freedom and the Fundaments clumped together to form the Fundamental planes: the Astral Sea, which radiates the Divine force, and the Elemental Chaos, which radiates the Elemental force. These forces in turn spawned the Gods and the Primordials.
They in turn created the Incidents, reflections of the Fundaments. They were:
Isolation from Connexion
Prisma from Time
Void from Thought
Death from Life
Spirit from Air
Vacuum from Earth
Cold from Fire, and
Blood from Water
The mighty Fundaments swirled together and made Balance, while the lesser Incidents eddied and formed Stability. Balance birthed Concordia, also called Concordant Opposition, which sat between the Fundamental planes and radiates the Primal force. Stability birthed The World, a fragile speck which nested within Concordia.
The Gods and the Primordials tried to circumvent Concordia, so that they might have influence on each other. However they could only do so when they acted simultaneously. This only happened twice, once by design and once by accident. When the planes touched the first time they formed the Feywild, when they touched the second time the formed the Shadowfell. These are the parallel planes that mirror The World.
The Fey and the Fell radiated Enchantment and Gloom, the essences which distinguish them from The World, and they shone through Concordia which focus them on the fragments of Astral and Elemental debris, causing them to germinate. But the Arcane force and the Shadow force were alien to the Divine and Elemental forces which had fallen into The World. They blended and made demi-forces, but those forces were unstable.
Divine and Arcane formed Benevolence
Elemental and Shadow formed Malevolence
Elemental and Arcane formed Caprice
Divine and Shadow formed Corruption
The demi-forces broke down violently, ejecting some of their energy back through Concordia, filling the voids between the Fundamental and Parallel planes and overlapping them. They are quasi-planes and connect the outer planes into a continuum. The remaining energy from the demi-planes absorbed Primal force and formed the four types of Mundane force: Ki, Martial, Psionic and Tech.
The Mundane forces settled, concentrating in different parts of The World, the majority of each force attaching to a separate continent.
Time passed.
Mortals fell from the mouths of the Primordials and dripped from the fingers of the Gods, and the mortals multiplied and spread throughout the Multiverse.