Nations of the North
Even though the farmlands of the south have fertile soils that can support all kinds of crops, and long, warm summers, they have their disadvantages as well. The diversity of life down south means more parasites and pests can get into the crops, and a larger variety diseases can infect the populace. Also, much of the American south is rainy and swampy, making it much harder to maintain crops, as well as structures.
North of regions like the Appalachian and the Chesapeake, growing seasons are shorter but the land much more fertile. This means that while there's less of a variety in crop, it can potentially feed a lot more people. It took a while for people to adjust to the bitter northern winters, but once they managed to adapt, very resilient people managed to emerge. The potential for higher, more concentrated populations was needed, because the Yankees live in a relatively more complex society. The soil needs the best medieval technology it can to function, so there needs to be specialized labor forces for ox-breeders and plow makers. The harsher winters mean houses and clothing have to be more elaborate. Stone cutters, lumberjacks and many other more specialized trades are needed to prevent people from freezing or starving to death. However, unlike in Hydraulic Empires, the greater and more diverse groups of people means that these bureaucratic societies aren't as autocratic. There's more compromise and politicking required.
Northerners generally eat more Old World Crops than Southerners. Corn isn't unheard of of, but the focus is on crops that grow in colder months, harsher soil, and to can keep over the fallow months. This means wheat, carrots, apples, and garlic. But new world crops like potatoes and squash are also grown. Potatoes are specially popular in the Pacific Northwest. Because a great deal of Yankees live near lakes or coasts, seafood is also common. It's usually popular to cook a mixture of meats, vegetables, and oils together in a kind of stew or chowder, and then serve them up in bread--either in bowls, or spread on large flat pieces of bread similar to pizzas. The emphasis is on stretching out the shelf life.
Aside from the annual blizzards, people in the North really don't have to worry about natural disasters, the priority is in making big, durable abodes that they can all pile in for the winter. Such structures tend to be made of sturdy oak or, if they can afford it, stone. There's a reasonable availability of granite and limestone in some of America's colder regions, so it's very common to build a house with the chimney or hearth being part of the entire wall. The use of stone is valued not only for the insulation from the hot summers and cold winters, but because firewood may burning for so much of the year, there's a higher risk for flammability.
The Northeast of the US is not blessed with much unique resources. Just a great deal of wood. However, the cash crops of the South and the minerals of the farther North, as well as the seas and rivers create trade network that cities can sprout up on. Also, because people of the North want to concentrate on exporting rather than importing, trades in artisanship are very important. In order to stay competitive with the relatively little they're given, these places make it a point to be the best as textiles, metal-working and wood crafting that they can be.
The Bible Belt:
Because everybody in the Middle Ages is very religious, the South's reputation for praying and churchgoing has lost its peculiarity. The North, however, has become something of a new Bible Belt. Largely, this is because there are a lot more District Supervisors of the Non-Denominational Church in the North, and so the Church has something of a Northern bias, and its denizens are more closely monitored. It should also be said there's more Churchmen to go around to teach literacy, and with a Northern bookmaking industry, this means the it's earned the Bible Belt moniker by virtue of there just being more physical Bibles and Bible readers per capita.