I took a look at the last posted save (1848), and I have a few suggestions that might be helpful next time:
1) Coal Plants. Most of your cities have Assembly Plants, which is good. But none of them have power! I switched all cities to Coal Plants (except one that's still building the Assemby Plant and one very-low-hammer coastal city). They'll take between 2 and 7 turns to permanently increase your empire's production by a third. In general, every city that wants a factory also wants a Coal plant, and it wants it right away (once in a while a health building has to come in between, or you get DoWed and don't have time, but otherwise).
2) Drafting. You're in Nationhood, and you've got large cities working marginal tiles (coast, plains farms, miscellaneous specialists). Turn 'em into infantry. Look at it this way: would you spend 140 hammers on something that returns 4 commerce per turn? That's the choice you're making by working two coast tiles instead of drafting an infantry. Oh, and build the Globe. It really is nuts.
3) Railroads and mines. Several hills have windmills, and you even have several bare hills in formerly American lands. Unless a city is really food limited, you want mines at this point in the game. Together with Coal Plants, you could have production about equal to Brennus'.
4) Biology. Not sure exactly when this should have been worked in, but fairly early (before Combustion? before Physics even?). You have a lot of farms, so it would have supported more specialists in addition to drafting.