Against which empires did Thayd and his mages rebel?
Here's what the lore says, drawn directly from the indexed sources:
-1087 DR * Thayd, a Theurgist Adept, leads a group of mages in a rebellion against the empires of Mulhorand and Unther. Thayd claims the northern provinces of both for himself.
Source: -1087 DR
-1081 DR * A band of rebellious Mulhorandi wizards open a portal to the orcs' homeworld using Imaskari magic. This eventually results in the Orcgate Wars five years later. * The rebellious mages of Mulhorand and Unther are defeated and captured. * The Theurgist Adept Thayd is executed for starting a rebellion in Mulhorand and Unther. He prophesies the decline of both empires.
Source: -1081 DR
-10500 DR * Miyeritar suffers the Dark Disaster, and is left as a wasteland in three months. Most elves of Faerûn are left shocked and horrified, leaving a four-decade-long fearful peace amidst the Crown Wars. Though history as written by the victors says otherwise, the High Mages of Aryvandaar are responsible. * Due to the Dark Disaster, the larger part of the followers of Eilistraee—a major patroness of Miyeritar—die in the cataclysm. This blow drives the goddess and her church into a near-powerless state, from which they won't recover for millennia. * The chain of islands that would later…
Source: -10500 DR
-105 DR * The Rus, an Illuskan tribe, travel through a malfunctioning portal and find themselves on the eastern edge of Lake Ashane. They soon integrate into the native Rashemi society. * The Rus berserkers trigger a Rashemi revolt against the rule of the demon lord Eltab.
Source: -105 DR