Tiberian Sun`s storyline followed the continuing struggle for world domination between the Global Defense Initiative and the Brotherhood of Nod, as well as the human race`s struggle with the relentlessly advancing alien Tiberium substance. Nod`s leader and GDI`s public enemy #1, Kane, resurfaces from an apparently faked death nearly 40 years after the initial conflict, which sets off the Second Tiberium War between the Global Defense Initiative and the Brotherhood of Nod. The game`s theme also subtly revolves around the question of why Tiberium came to Earth in the first place, with the discovery of what appears to be an alien spacecraft and a mysterious object known as the Tacitus.