Custom Civs not loading in a Custom Scenario

[JFD]

I would just like to ask anyone who knew how to solve the issue of getting a custom civ to load in a custom scenario. Currently, if I were to, say, add my Papal States civ to a generic map, if I were to go through the Mods menu to load such a map no custom civs show up as being avaliable to select. Instead it is just Random Player. Thanks for your help in advance. A solution to this issue would help very much.