It is the year 2047. The GDI has defeated CABAL and Nod rarely appeared as foes. GDI had trouble with Tiberium again and 50% of the Earth is a yellow Zone. 30% is the Red Zone which only military can be allowed there and 20% is full of high tech stuff and healthy rich people there. Nod on the other hand are secretly being prepared to strike back at GDI at anything necessary.
The Brotherhood had control the Yellow Zones and build new Avatar Warmechs a giant laser monster that can rip up tanks and anything off the ground.
The GDI however got new anti tiberium weapons and now retire most hover vehicles and walkers in favor of all terrain tanks.
The Scrin are awaiting till the human race is exterminated and so they can harvest the Tiberium off the Earth.