well lets see quick rundown on the forces

china, gla and usa

china:

tank pwns all, it's double turreted and you can build a gatling turret, bunker or umm...i forget on top. slow as hell but they get the job done, especially with gatling turret. infantry builds 2 at a time (red guard, your grunts) WMD is a nuclear missile. their air power is a mig that holds 2 fire missiles

gla is what i like to call al queda. they've got trucks with mgs, scuds with he or anthrax warheads, bomb trucks, tanks that can scavenge parts to upgrade their guns, tank shells with anthrax, anthrax upgrades, tractors that spray anthrax. scud storm is a cluster of long range scuds that launch a shitload of anthrax. yep they love anthrax.

us by far is my favorite. you use chinooks for picking up supplies but they can also hold infantry, 8 of them. rangers (your grunts) can load up and repel into the combat zone or into civilian buildings. biggest air force in the game, f-22 raptors which carry 4 "mavericks" i shall dub them, arora bomber which carrys 1 big bomb, f-117s which i haven't messed with yet and commanche gunships which carry 4 missiles with a chaingun and can be upgraded with rocket pods. fun fun.