The Great War was the name given to the conflict between the Ancients and the Tolgath. It raged for years and finally culminated on Ulgrotha with a battle known as the Great Destruction. The war ended when the young Tolgath Ravi rang the Apocalypse Chime, without knowing its real effects, and created the Dead Zone, killing almost every creature on the plane and destroying the mana lines of the world, leeching them off through the rifts the war had caused. Only a small portion of the world remained inhabitable, since it was fueled by a rift to another plane opened by an Ancient wizard defeated by the same Ravi. Just ten human generations later, the history of the Great War was almost forgotten, since on Ulgrotha there wasn't a single written language to record it. Only the dwarves seems to have understood that something terrible happened on the plane where they are trapped, and are trying to put together the fragmented pieces of the history of the Homelands.
It was through these rifts that the war would affect other worlds throughout the Multiverse. It disturbed the stability between the spiritual and physical realms of Kamigawa, leading indirectly to the Kami War. The peal of the chime also created a connection between the Talon Gates on Dominaria to other worlds, such as Kamigawa.