Now, I used to reveal the world history plot-line via ancient scrolls that had to be specially translated. It's a good way to slowly unfold a story with not much exposition. I'll give examples of some I used for another campaign.
Scroll 1: All planes are connected. Home Worlders can shape magic since the Light World is within the Outer Chaos
and Dark World spheres. They must be trained in the matter of doing so, though, or have Dark World blood. Casting normal
magic spells will not cause deterioration of the Home World. Corrupted Dark Worlders using magic will.
Magic is nothing more than the malleability of the planes. Magic is essentially the shaping of unstable planar matter.
The more malleable the plane, the easier it is to shape. Magic is neither good or evil at it's core.- Creatures native to
the Dark World are born with inherent malleability. They automatically have a connection to the Dark World no matter
where they go. This allows them limited magic use even on the Home World.
Scroll 2: Chaos deteriorates reality around it, corrupting what it touches. Creatures influenced by the chaos can
only become corrupted of their own free will. Still, the power the chaos offers incredibly tempting. Accepting the
corruption will give one enhanced abilities depending on the creature.
Now, if we do play, I may bring elements of the campaign setting I did back, but it's ultimately up to who's playing, DMing, etc. Also, I'm always open for criticism, so feel free.