Great War
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 widely as the Great Destruction. The war ended when Ravi rang the Apocalypse Chime and created the Dead Zone, and destroying the mana lines of the world, leeching them off through the rifts the war had caused.
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.[1]