Already used to the old nations in CotA? Replace them with 7 new ones! The New Nations are:
Simply overwrite your "Data" folder in "Paradox Interactive/Commander/" with the "New Nations" Data folder.
There is also a "Backup" folder in the Zip file, containing all the original files. If you want to play the normal game again, simply overwrite the Data folder with the one in "Backup"!