I chose not to include matriarchy because there are no known matriarchal societies in world history, and I want all elements of Civilization to represent authentic elements in world history (though combinations of elements is allowed to be fictional). However, I played with the thought of introducing a "Radical Feminist Bureaucracy".
Right now I am trying to balance out these civics, so that each would be the most useful at some occasion. Suggestions?
http://en.wikipedia.org/wiki/Matriarchy
