Ah what the hell
Way back at the beginning there were the Primordials, they created Creation to be their little sandbox to play around in and being lazy, created the Gods to run it for them. Think of the Ancient Greek Titans and you've got the basic picture, the specifics aren't too worth going into right now.
Now the Primordials weren't the best rulers as things went and the Gods plotted to overthrow them, namely the Celestial Incarnae who were the greatest of the Gods; The Unconquered Sun Sol Invictus, his counterpart and closest peer Luna, and the Five Maidens; Mercury, Venus, Mars, Jupiter and Saturn. However the Primordials were cautious of the possibility of betrayal/rebellion and took appropriate precautions; when they created the Gods they made sure to program the complete inability to harm their creators into them, this Geas rendered the Gods helpless against them.
But one day one of the Primordials, Autochthon the Great Maker, stumbled across the solution, Autochthon was the runt of the Primordials and constantly bullied and pushed around by the others, he was also deeply enamored by humanity as he identified with how they were so small and weak in comparison to the world around them yet so driven and creative, this eventually led him to create what is known as Exaltation. Due to his mistreatment by his fellows the Celestial Incarnae were able to convince him to help them and turn on his brethren and so he gave the secret of Exaltation to them, this allowed them to bypass the Geas preventing them from harming their masters by imbuing mortal vessels with sparks of their own divinity to act in their stead, Exalts.
Exalts are the chosen of the gods, they were their warriors in the war against the Primordials, each Celestial Incarnae creating their own form of Exalt; Sol created the 300 Solars, Luna created the 300 to 400(ish) Lunars and the Five Maidens created the 100 Sidereals
Among them were also many, many more Terrestrial Exalts, the Dragonblooded, who were created by the only other Primordial to side with the Gods; Gaia the Emerald Mother (to make a long story short she and Luna fell in love), to serve as the army to the Incarnae's generals
Autochthon also did his own thing off to the side and made the Alchemicals
After the cataclysmic war for Creation was over the Exalted came out victorious either slaying their Primordial enemies or imprisoning them within their own king who basically became hell. The Incarnae withdrew to take over heaven leaving Creation to the Exalts to rule over. Unfortunately the imprisoned and dead Primordials (they can't really die as Creation wasn't built to accommodate such an event) bore something of a grudge and uttered the Great Curse as they fell which afflicted the Exalted as a final parting gift, it affects each of the Exalted differently but for our purposes we really only need to know about the Solars. Over the years as the Exalted rebuilt and ruled over Creation the Great Curse, which went unnoticed by everyone, slowly drove the Solars mad, it twisted their virtues and magnified their flaws warping them into insane tyrants. Faced with the prospect of these mad god kings destroying everything the Sidereals and Dragonblooded came together and ultimately decided that the only solution was to kill every last one of them and trap their Exaltations so they didn't reincarnate (When an Exalt dies their little spark of divinity leaves and eventually seeks out a new person to bond with, each kind of Exalt has different parameters for who they will bond with).
The Lunars were somewhere between bystanders and collateral damage for the most part, most of them fled the carnage.
Since then the Dragonblooded rule a large chunk of the world, preaching the Immaculate Philosophy which states that Solars and Lunars are actually demons pretending to be the chosen of gods, and hunting down any that surface where they can find them, the Sidereals manage things from the shadows
