after saving the world and defeating Steppenwolf, another kryptonian came to planet earth and revealed to the world that Superman is an alien, and this causes Superman to start having haters, in addition another alien appears and talks to Superman about not being from this planet, Zod is actually came to planet earth in search of Superman because in his dna he has the Krypton codex, and using the Zod codex he could bring Krypton back, but the only way to do that is to turn planet earth into Krypton by force , and obviously Superman won't let Zod accomplish this feat.
