This was posted on the Facebook group @amazingmaps, and it's a very good study reference point when trying to avoid making Medieval America strictly based on the Middle Ages of Western Europe, despite the culture of the United States and maybe especially Canada coming from a particularly Anglo-Eurocentric basis. As White stated on the climate page, cultures in pre-Industrial societies are subordinate to natural phenomenon of the world around them.
In general, it's important to look at the states' Old World counterparts in the pre-Industrial societies--what they ate, what they wore, and how they waged war. Once again, it's not always a one-on-one comparison. Below the Mason Dixon line would be a lot less centralized than China, even during its Three Kingdsom phase, and conversely, Feudal Japan was a lot less centralized and maritime than the East coast. But it's still fun to compare, and always important to keep in mind. Funny enough, there's no region that matches Italy--home to the iconic medieval republics. Because Africa is not considered, they don't make one on comparison to place like Egypt and and Morocco, which probably more closely match the southwest than India, and that White himself name-dropped.
I would say when imagining life in Medieval America, there's four things to consider; These four things would meld into kind of a gestalt, and there you have you Med-American countries.
-The cultures of the old world with most similar climates.
-The cultures of the Indigenous people that preceded European settlement.
- The way of life post-settlement for its first generation or so, or at least until mass industrialization.
-And perhaps least significantly, but not to be forgotten, the ethnic makeup and memory of that places right before the relapse.
