Some ideas for next expansion.

[jUNGLE cHRIS]

Biological and chemical warfare! Biological weapons with the discovery of biology and chemical weapons with the discovery of chemistry. In the late game, these could be loaded into missiles.

 

[ljofa]

I'm not sure how you can get civil war to work successfully - maybe cities with great people can rebel if there aren't enough city improvements corresponding to that great leader.

There could also be civil wars linked to the spread of religion - if enough of your cities don't have your state religion they could rebel.