Well, in Generals, there was diversity between China and USA. This is not IRL. :P
Despite that, I was thinking, what if the USA has become drone-centric now? None of the vehicles the EU has so far look like drones. What if the USA is no longer a huge military, but rather has gone towards robotics instead? Their faction could be based on more subterfuge or strong but weak vehicles with some commandos on the side? Perhaps they could even be spam-based instead?