Zardnaar
Legend
Going off 2nd edition rules where races like Orcs didn't have spellcasters, and reading Rise And Fall Of a Dragon King and how they went about exterminating the races, yes Orcs would've gone down easily. Unlike normal defilers, the sorcerer kings are actually dragons, immune to normal weapons, and can use animal life to cast their spells. They are basically gods on that world, and with them leading armies exterminating tribes of orcs, you can see how they could fall quickly. The thing was though, each king was tasked with eliminating a single race at a time and did so at their own pace (some were lazier than others), they stopped when found out that they were doing this to create a halfling only world, not human. (ALL sorcerer kings were originally human since halfling couldn't learn magic). So the races that are still alive are the ones that they didn't get to yet, or didn't finish their genocide when they learned the truth about what they were doing.
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Some of the SKs were statted out in 2E. They are roughly as powerful as an archfiend, they are weaker than a few avatars of the god of Faerun for example.
In 5E terms The Dragon would be CR 30, while the rest would be CR 21-24 or so which is roughly on par with the archfiends. SOMe might be CR 25/26 depending if you like the 2E or 4E take on them.
The cleansing wars lasted 1500 years.