The shopping mall is a bit lame, but I honestly can't think of a better idea off the top of my head. If I were to make an American civ from scratch I'd probably give it some type of air unit as its UU, the only problem is the game is pretty limited in what you can do with air units so I wouldn't want to go in that direction either. Someone suggested an early Marine unit (maybe replacing Grenadier). I agree that, in civ terms, the Navy SEAL is kinda stupid. It's not like there are huge armies of Navy SEALs, which is a possibility in Civ.
The Minuteman is another possibility, but it has been done to death and to be honest I don't really think they were much of a great force anyway. I mean, they were notorious for retreating and weren't well-displined enough in my opinion to be a UU.
I remember posting a suggestion of changing the Grenadier to an American Gunslinger.
A "Billy the Kid" type of unit with 2 revolvers. Perhaps, a Grenadier with 2 first strikes?
I realize these were not truely abundant, or used to defeat armies, but, it has become an icon of American culture since the 1800s, and very well known world wide.
I was thinking a Factory with +50% Aircraft production.
America did build a huge number of bombers and fighters (B-17s, B-52s, P-51s etc)during the World Wars.
Building this and the Airport would give them more aircraft to defend their coast and carriers with.
Also:
Since, The Goths defeated Rome After Rome came to power and conquered other lands. It would make since that the Goths should have a varient of the Maceman.
Perhaps, the image can be mounted-like, similar to the Immortal. Instead of increasing their military production, I would simply make their maceman unit 25% cheaper, and only require Copper.
This way you can pump them out and take out swordsman easily.
Making them based on the horseman, creates their unit before the unit they are suppose to be able to conquer.
Consider, The Mongolian Empire was the largest Empire in History, even to this day. Yet, you are setting up the Goths in the same time period, and with the possibility to defeat the powerful Mongolians.
This might be why, Numidian Calvary is a Base 5 unit.
The Goths did defeat a weakened Roman Empire, but, they didn't create an empire that lasted several centuries or more and are indeed gone now. We need to keep them in perspective.