I would fix this problem like they do in civilization 4. The further the city is from your capital the more upkeep it cost. More cities increase the upkeep. So this makes a bigger empire harder to manage. You can prob also make slider how much you pay your army, like you can have a small but verry high moral army, or big and low moral army. Wich at the end cost the same and has the same strength.
Also make units have upkeep. More units, is more upkeep. So add income and upkeep!
I played your game before, tried it now again and you should add maybe buildings. Like make it you can specialise your city. Like, this city is good for producing army, another good for income. Some other maybe better at making tanks, other better at making boats. Its an online wargame, but it needs buildings imo. Just some ideas. I like where its going, only need better interface and map. But the idea behind it, i like it, its my kind of game i like to play:D
Thats my feedback so far.