Here is my list, its not actually what i "want" to have, but actually a list i can remember now without consult of all civilizations that still are missing (no matter thier size or importance
Maya - was the only of the 3 (Aztec and Inca) witch was not a true "empire" but a high advanced society for its time, still they fought the spanish
Celts - there is a mod but i still not tested it
or instead add Scottland and Ireland (would be illogical to have them 3 since those last two CAME from the celts hehe)
Apache - they fought the Americans for their lands, and if i dont mistake also against british and french too; i wont google cause it will loose the fun
Norway - since they put the denmark they can put Norway too
Brazil and Portugal - its my country and it as old as America so i must add it

, we had some wars here too
(just a few thou hehe, most of the action on south america along the history was along the west coast, majory the spains against the incas, then later the spanish against Bolivar leader and lots of spanish countries like Peru, Colombia (Great Colombia), Bolivia and Venezuela. And about Portugal it would be nice too, as special units could have the Bandeirantes.