empire earth does that, but it concentrates on 10 or so different ages instead of one so as you can imagine gameplay is not that deep. Nevertheless, it still a very enjoyable game.
i have empire earth, its xpac, its sequal "empires" and rise of nations...they are all good games...but im looking for an rts that is STRICTLY a ww2 era game that plays more like c&c generals/age of empires 2 you know?