Cahokia I mean was impressive but... by North American standards only, if you factor Mesoamerica it already pales in comparison, add old world stuff and it kinda just because a grain of sand in a desert. In any case there were probably more settlements like Cahokia around, they just have now cities on top of them now given how logical it would be to have settlements mirror ancient ones. In any case I think this rebound could take up to 1800 AD. when I think the Ice Age is gone and farming becomes easier and more different crops become universally widespread.
I´m not sure if you could have a native Cortes, for example look at Alexander, his empire went only for the organized civilizations, not northern into the Balkans, I think you can have massive conquest only if you have the local structure to keep the areas conquered(reason why you couldn´t easily deal with nomadic people as a settled farming country or civilization)
But we don't know those sites. St. Louis was built on one of what seems to be Cahokia's tributaries, it was not as impressive as what as at Cahokia, nor were East St. Louis's mounds which lasted slightly longer and had the same origin (which interesting were inhabited slighly longer). If there ever was a settlement as impressive as Cahokia north of Mesoamerica, it would've been recorded by Europeans as it would've been bulldozed (unless other American Indians would've destroyed it, which seems unlikely since they seemed to have leaved the mound sites alone). Many Mississippian etc. sites have been built upon (since they're good land), but Europeans tend to have recorded the mounds, or otherwise have ignored them and built their towns elsewhere.
The point is, Cahokia is the greatest site north of Mexico, and a hint at what the Mississippians as a cultural whole could accomplish. Oftentimes you see "Aztecs, Maya, Inca" for three major American Indian cultures--the Mississippians might as well be the fourth, and population density-wise, seem to have been developing on that level. As I said, imagine Cahokia in every decent-sized city in that cultural network which spanned the Southeast and Midwest, and into the Great Plains. That's cultural evolution, like how the Mesoamericans/Andeans had to develop up to the level of the major temples, city sites, etc.
What different crops? From what I understand, you'd need a full Andean-Mesoamerican exchange to get quinoa, etc. in North America. Unfortunately for the North Americans, they mostly abandoned their native crops. Unless you have European crops, of course, which add another dimension but carry that whole destructive element with them.
By a Cortes and Alexander, I mean an individual with the capability to change the course of history. Which suddenly it isn't just once city in the Mississippian region, it's multiple cities under the "rule" of one person, and by that I mean like we consider the Aztec Triple Alliance an empire, the Inca an empire, etc. Maybe it's more like Sargon of Akkad in Mesopotamia. But either way, it's someone making an empire. It's potential development of the Mississippian region. All these sites seem to have had a similar culture (though different languages), so it doesn't seem too far different than the situation in Mesopotamia in that regards.
Probably, but the fact that llamas evolved as mountain animals, while horses evolved on the plains, means they will always be inferior as long distance transportation. Personally, I don't believe that some animals are "completely un domesticatable". even zebras, with enough time and selective breeding could become pets. But post-ice age mega-fauna die off really limits the possibilities in the Americas.
You'll like see llamas bred for fur, milk, meat and light pack use, but long scale travel would be very difficult.
You will see a proliferation of dog breeds with some very large breeds arising for pulling sledges, hunting, and war.
If dogs aren't suitable for clearing out rats, then bobcats might do the job. There's some intriguing burials of bobcats with people at some Mississippian (I believe) sites. In theory, a domesticated bobcat could be trained like an attack cat to threaten intruders, as well as the purpose of hunting rodents.
But yes, dogs are the obvious choice. The Salish wool dog is very interesting and a hint at what they could do. But I'd question why there weren't more dog breeds developed OTL for those purposes.
The best domestic animal might be the reindeer, going by Siberian examples. The woodland caribou is native throughout Canada and into the northern United States. Could be a good pack animal. There's also the moose, which according to Soviet efforts, is in theory domesticatible. Since both would be domesticated at a late date, and neither seem to be suitable for the same uses the horse was for the Plains Indians, there truly is no horse substitute in the Americas. Not that the caribou or moose won't dramatically change things for where they're at.
