Scars of Faerûn
Abeir was one part of the prehistoric planet called Abeir-Toril.
After the Primordials created this world, the gods interfered by wanting to create living beings to live on Abeir-Toril. This sparked a war of unbelievable destruction which ended when Ao separated the world into Abeir and Toril, each located in their own material plane.
From then on, the gods rule Toril and the primordials rule Abeir.