The Mississippians of course, after that Iroquoians/Haudenosaunee because the story of Hiawatha and the Great Peacemaker would be a cool campaign without Europeans.
For the Other section I choose Algonquians, I see as a ābridge civā like I see the Tupi.
I also have a few suggestions for Historical Battles, because there is more information than most people think.
Ani-kutani (~1100) is a Cherokee story (they are part of the Iroquoian language group, they can be depicted by the Iroquois/Haudenosaunee, but Mississippian will also work because they were part of the mound builder culture).
In this story the Cherokee tell how they rise up against the mound builders and there cruel priesthood, after their succes they promised each other they will have never have such hierarchical society.
I imagine it work out similar as the Age of Empires I Yamato campaign Coup where you need sent tribute every X minutes to your overlord in order to keep the peace, until you are strong enough to defeat them by destroying their wonder and castles.
The Mississippian kingdom of Joara and explorer Juan Pardo (1567ā1568), he build six forts (castles) in present day North Carolina. After he left, all six forts are destroyed and burned down by the Mississippians. On the largest fort they also build a mound. After that the Spanish never returned that far north.
I images every fort/castle you destroy as the Mississippians gave the remaining Spanish forts a bonus like the tec Citadels and Fortified Bastions.
(The Wooden Fort we have seen in the Tupi promotion would be perfect for the it).
The Warrior Maiden could be an Iroquois/Haudenosaunee Historic Battle.
The NarvƔez expedition (1527) could be a from point A to B Historical Battle
Etzanoa and the retreat of Juan de OƱate (1601, I know just too late).
The story of Pahtahnkum could also be worked out as possible a Historical Battle.
Crow Creek (~1150), my idea for the scenario need a bit of cultural background explanation that need to be told in the opening narration.
In a lot of North American cultures you can be adopted in to their society if you are needed/worthy, the narrator is adopted in the Crow Creek settlement, but when he was out hunting and standing on top of a cliff, he see a big war party approaching under the cliff. He recognise that the war party is part of his old society.
In game you control a Mississippian scout unit and need to decide to run back to Crow Creek settlement and help to defend it, or run to the war party camp and join up your old group and attack Crow Creek.
To win you need to build a wonder if you decide to help the defenders, or destroy it if you decide to join the attackers. There is a side mission to gain/prevent the tec Atheism that add 100 years to the wonder.
The Attackers could have acces to Haudenosaunee units and UT, while defenders keep the normal Mississippian Tec tree.
And lastly, of course it would be cool to see the Viking encounter from the Native perspective, the Algonquians are the best candidate for that (because where Vinland suppose to be, however if you want to have the story in and around Greenland, then Thule scenario only units would also work in my opinion)
Wahunsenacawh (the father of Pocahontas) with his brother Opechancanough could be an interesting historical battle before the British arrive, they consolidate power of other towns and were leaders of a Confederacy before the British arrival.
Also the story of Paquiquino and the burning down of a Spanish Mission in 1571 and the Spanish revenge of it, would be a cool story beat in that scenario.
Or if we are willing to go past the 1599 mark, a cool campaign.
Also with the inclusion with the Tupi, the TaĆno and other Caribbean people as the Arawak could become a possibility, if I might speculate, the dev might have them already in mind because the Tupi did not receive a blow gun unit, leaving it as a possibility for this area.
Also the natives in Florida are really cool like Timucua and Calusa, they were very effective fighting of the Spanish and French.
Because I never considered them a possibility for the game before, I did not keep as much notes about them as the rest. Still I know there is enough materials for cool campaigns and Historical Battles.
I think the Mississippians, Caribbean and Calusa/Timucua could easily share the same Mount Building Architecture, while the Haudenosaunee and Algonquians should have their own Woodland Architecture. That means there even might be enough material for two North American DLCs, before the Tupi I never thought that could be possible.
I assume you wanted to write 1540? In that year De Soto was on the loose in the Mississippian heartland.
I would recommend to give the The Other States of America podcast a listen, season four talks about Ponce de León (1513-1521) till the chiefdom of Powhatan (c. 1545 ā c. 1618) there are a lot of campaign and historic battle inspiration there.
But he talks in great details about the early days of Europeans in North America and the world before their arrival.