It does start off like that, but I think after you start an industry within your city, you gain access to empire management, where you start organizing trade between other cities, building roads, managing armies, etc. It's been a long time though, so I might be misremembering.

It's really mostly the cities, outside of the city management is really secondary (at least in Caesar and Zeus which I have played the most). I strongly recommend the whole series, they are really great games.