I know that the Spellplague caused Abeir and Toril to merge, but I think that the First Sundering might be a process that split Abeir-Toril into two (because the Second Sundering involved Ao recreating the Tablets of Fate and "separating the worlds of Abeir and Toril once more").First Sundering at Forgotten Realms Wiki wrote:The First Sundering (sometimes simply The Sundering) or Ever'Sakkatien (as called by the Tel-quessir), was a High Magic ritual cast by the greatest High Mages of the Tel-quessir during the period of The First Flowering, around -17600 DR.  The ritual resulted in the creation of the Isle of Evermeet, but also resulted in widespread disaster which destroyed or altered much of Faerûn and may even be the cause of much of the non-uniformity of the Weave throughout the continent.
Ever'Sakkatien is somehow connected to the more recent Second Sundering, an event that takes place in the 1480s DR, and with the Tearfall, that took place in -31000 DR.
So, what I'm wondering is: is the First Sundering restricted to Faerûn or did it effect all of Toril (or all of Abeir-Toril)?
Could the First Sundering have had effects across Realmspace? If so, what sort of things might have happened on other worlds?
What sort of stuff was banished to create Evermeet?
Is there anywhere in Realmspace that could regarded as an "Evermeet of Wildspace"?
Sword Coast Adventurer's Guide says that there were empires of reptilian, amphibian and avian peoples in the Days of Thunder (and that their empires fell apart, leaving lizardfolk, bullywug and aarakocra tribes). Could there have been wildspace reptilian, amphibian or avian civilisations that got distupted by the spell cast in the tower built on Faerûn?
Could any of the locations destroyed by the First Sundering (like Atorrnash) have been thrown into the Sea of Night, rather than destroyed outright?