General Zod of Krypton was banished to Nullspace following his genocidal actions during Krypton's militaristic expansion. For tens of thousands of years he and his two closest lieutenants were caught in a crystal prison that contained them indefinitely. After eons of being trapped in the void, Zod was discovered by the creature known as Annihilus. The insectoid warrior was persuaded to travel to Earth to find the last vestiges of Kryptonian technology, and secure the means of breaking open the prison.
In 2010, Zod was released on Earth and with the aid of Annihilus and his armies, began conquering the planet. His attack was thwarted by Superman and several other allies who joined together to defeat the would-be Emperor. They were unable to imprison Zod again in Nullspace but the combined forces were able to route Annihilus' armies, steal the insectoid's Control Rod, and send him and Zod scurrying into deep space.
The fallout from these battles caused extensive damage to the East Coast, notably triggering the disaster zone that would become known as No Man's Land in Gotham.