Nearly every major threat of my campaign can be traced back to its historical origins, though the history is murky and hard to follow at times. There's a good reason for every major event, and many of them are linked together. I haven't nailed down all the details yet so it's hard to say too much without potentially restricting myself too much, but here's a shortlist.
Long ago, the genies ruled the world; the celestials claim genies and other elementally-aligned beings (like dragons) were essentially uplifted from ordinary mortal existence to help shape and maintain the world and its inhabitants. These uplifted individuals have sometimes gone astray...like the genies.
The genie-rajahs mostly ruled with tyrannical indifference, if that makes sense. They kept mortal races as slaves, some treated their slaves well, others treated them very poorly, but in general humans(/etc.) weren't allowed to independently own property, couldn't marry without their master's permission, and just overall had really restricted lives.
Mortals living outside the cities have a hardscrabble life, but the Kahina--druids and shamans--help them survive, even thrive out in the desert. This raises them to a position of great prominence, and some of the modern Nomad tribes are still ruled by druid (or, more rarely, shaman) chiefs. This also makes the Kahina rather more politically and socially active than the usual perception of druids.
Some terrible event happens. This fundamentally changes the world. The powerful ancestors of the elves, whom the people of today call the "El-Adrin," departed from the world and took their cities with them in order to avoid this change. The genies also departed, but left their stuff behind, and remain accessible in the elemental otherworld, called Akirah; their country is called Jinnistan. This is also--not coincidentally--around the time that evidence of the mad Cult of the Burning Eye begins to appear.
The First Sultan, a mythic figure that some believe didn't really exist, but the party has evidence that he did, rose up sometime after the terrible event, but before the genie exodus, and played a pivotal role in taking genie cities and encouraging a thorough exodus. The party has learned that he had three wives: a human wife (from whom many of the modern-day merchant class descend), an orc wife (from whom many of the modern-day Nomads descend), and a genie (specifically an air genie) wife, whose descendants are not yet known.
Around this time, the celestials also completely depart the world, and the Safiqi Priesthood comes into existence. As mortals take over the now-abandoned genie cities, the Waziri mage order comes into being, and the Kahina slowly lose prominence as city life becomes much more common than nomad life.
A heretical group--originally part of the "internal police" branch of the Safiqi priesthood--breaks off sometime about 2-4 centuries after the genie exodus. They become the Zil-al-Ghurab, the Raven-Shadows, who believe that true enlightenment can only be obtained through taking someone's life when they don't expect it. The Safiqi have tried to stamp them out ever since, and every time it seems like they've succeeded, the Raven-Shadows pop back up again a few generations later.
Much more recently, about 400 years ago, a rift occurs among the druids (but not shamans): wishing to reclaim their former prominence, they begin using powers attuned to the Sun and the Moon, and a internecine conflict breaks out between these warring factions. A druid of the moon falls in love with a druid of the sun, and the two of them have a secret romance and produce a child, hoping he will be the great uniter of their two disciplines...unfortunately, their son cracks under the strain and runs away, only to later return as a dark and twisted being leading the Shadow Druids, who revere death and decay and want to transform the region from semi-arid to swamp so they can exist forever beyond the boundary of life and death.
Around that same time, a black dragon secretly immigrates to this area from their homeland, running away from good dragons hunting them. They have slowly built up their power, intending to rule the largest city of the area as their "hoard." This went unnoticed by the people of their homeland until very recently, and the hunt is now on.
There are of course puppetmasters and manipulators behind the scenes,