I wanted to take a scenario (the earth huge) and add all 18 civs since it only comes with about 9. But in the world builder, I can't find a place to add civs to the map that are not already included. For example, I want to add the Americans, but they aren't in the "player mode", so I can't add units. How do I add civs that aren't in maps already, such as with this map? I'm sure its an easy fix, just some button I'm missing for some reason?