Tiberian Sun takes place within an alternate timeline involving two factions - the Global Defense Initiative (GDI), and the Brotherhood of Nod - and an alien substance called "Tiberium", and occurs after the events of Command & Conquer. Tiberium has become a serious problem for the world since its arrival in the 1990s, not only in causing a conflict between GDI and Nod over control of the valuable crystals it creates from leeching precious metals from the soil - leading to the First Tiberium War - but also allowing the substance to slowly spread and terraform the planet's ecology and landscape, including causing mutations in humans, the formation of new alien lifeforms, and the development of new weather patterns called Ion Storms.

By the 21st century, GDI is focused on researching the means to combat Tiberium's spread, making use of an orbital space station called the "Philadelphia" to command its forces, while Nod has splintered following the presumed death of its leader Kane, with both factions working to develop new technology to provide each with equal strength in their armies, including armoured walkers, cyborgs, advanced defensive measures, and armoured infantry. Read more.