The Feudal Core is an interesting region of the map. Unlike many of the other sections, this isn't necessarily categorized by geography, so much as the social structure (Although it's also called "The Heartland" in many files". Pretty much all the nations in this area are governed in a feudal society, with 14 of the twenty major feudal kingdoms. It's also, in many ways, the core of America in general. It's mostly eastward, but moving somewhat towards the middle, and as many as 28 million (nearly half the population) live there, it's essentially the Western Europe, China or India of America.
The area is really the meat and potatoes of the continent, but White has given us so little information on it. This is possibly because 1) It's so vast, or 2) We're well aware of knights an royal courts. We just have to imagine the regular model, only influence by Dixie or the Rust Belt. In fact, the interesting thing is that it has an icon for both Northern and Southern lifestyles. It's hard to truly peg the region's culture. It's most likely a gradient or flux, from nations that are barely distinguishable from Canada. to those that start to look Caribbean. Cowboy culture may also have an effect on the edges too. It's very likely most of the continent speaks a derivative of English, though obviously the fringes are going to flirt with other lingua franca. Most of the core is inland, and cleaved by the Appalachian mountains. Water transportation is made through the Great Lakes (which will get their own entry) and the main rivers that stream across the land; Most of all the Mississippi. It's mostly agrarian in nature. In the Feudal core we see a grain belt, a cotton belt, and a tobacco belt. This is all in contrast to the exotic trade of the gulf coast, and the crafts and fish of the northeast.
Iowa is the only feudal core nation mentioned, and perhaps betraying White's fascination with the herdsmen, it seems to basically be a kingdom that resulted from cowboys kicking everyone's asses really hard. Like other places, this seems to have a pretty distinct parallel--barbarian tribes that eventually went native, like England, Hungary, and a few others. Of note, Chicago is within its borders. It was once a major city, and it still seems to serve a purpose as a major Great Lake port, and maybe one of the windows to the west.
Ohio seems to have absorbed Indiana and Kentucky, and may be the central power of the Heartland, maybe the continent. Inside its borders you have three important trade cities, six, maybe even seven million residents, and as many as four district headquarters for the Church. The Iowa page shows that it did a decent job of defending itself from barbarian invasion. How did Ohio, once considered a generally average state, come to such power? Well, it's that exact averageness. The soil page shows it has some of the best soil on the continent. West, it can e a breadbasket, and south it has cash crops. To the east, a good amount of mineral wealth to be a fair player in the industrial age. It's surrounded by rivers and mountains that could make for good natural borders, transport and defense. The region basically has just enough of everything to sustain itself in a medieval era. Politically, it probably most resembles France.
Surrounding Ohio is the much less stable area of Tennessee. This is may be the most balkanized region of the continent, and "Balkan" may be the operative word here. This might be a good place to mention how many of the Ozark and Appalachian regions are split into a wide variety of territories. I can imagine something akin to the Scottish Highlands. We see communities that are very extremely clannish, and it's somewhat tricky terrain has probably kept it from being fully claimed for Ohio's empire. In any case, we see three flags for a relatively small region, and the east map shows the state has been split up. We have Memphis, the important trading city, and probably a lot like the Deep South nations in culture (The state called Shelby County, possibly the star on the black background); Knoxville, an isolated Appalachian burg, and Nashville, the spiritual center of the region, found in Tennessee proper (With, I'm assuming, the original flag).
However, the most western flag is a green flag with a horseshoe mark This may be Missouri as Iowa's page seems to say Shelby had a hand in rebuilding St Louis, so the area as a whole may generally be considered a colony of patronage of Tennessee, hence its classification in the area.
Piedmont is an interesting case study. It appears to be the only area in the core to have total coastal access, although the US's presence, and very swampy east coast has kept them from building there too much. We do have the coastal port of Charlton though. Piedmont is named after the valley in the Appalachians, and from what I can tell, it seems a modest but healthy region. It may feel the most "European" of the Southern nations, due to its place on the Atlantic seaboard, and its proximity to the Yankees. It probably has decent relations with the Church, and is not a racial anomaly--it may not even be a large place of conflict. In fact, the warfare map shows that they don't seem to be even fighting anyone. Piedmont is possibly the most peaceful and pleasant region on the continent.
The Deep South comes next. it's symbolized by two flags, both with crosses. One is Georgia's flag, and more or less the symbol for the Confederate States, and Southern Pride in general. The other looks like a more colorful version of Alabama's flag. The area evidently includes Georgia, Alabama and Mississippi, more or less, forged into two large nations and a smattering of smaller ones. It's hard to tell how many people populate the two countries, but it's as many as 10 million, probably knocking that down a bit to seven million between them. Mostly feudal in nature, it seems in the southernmost regions, we do have a few Secretarial State-type fiefdoms. What's interesting is, two of the cities on the main map have the Confederate flag symbols to mark them, probably indicating Georgia thinks of itself as a very special case. When civilization fell, it's possible nobody felt more elation than this region at the opportunity to pursue their own destiny. With secular and federal institutions out of the way, they readily embraced the chance to reform the south as it "should have been", autonomous, agricultural, and status relying on land. The antebellum period is probably looked at as a model, and for better or worse, is very applicable to this new era. This is the hottest region of the feudal core, and while White says that they wear as little clothing as possible, I think that might not be the case for this particular region, especially in the Northern parts, and with the upper classes, as to distinguish themselves from the country bumpkins and the snake worshipers. (Most of the major cities are not in the hottest regions). I think there might be a little more light clothing. Possibly tunics and stolas. The Deep south may very much resemble Ancient Greece, at least in apparel, and possibly architecture, due toe Georgia's famed marble.
Finally there's the Southern Frontier. Or it may simply be the Southern Front. The two flags pretty much indicate what it's about; Holding up their end of the religious world. One is Arkansas's flag with a cross, and another is the flag of St. Magnus, with an alligator on top of it. If you'll look down at the religion maps, you'll have a good idea of where the Southern front It's probably more or less the regions west of the Mississippi River and south of the Missouri River. These are bulwarks of the Non-Denominational church, and are likely on their own. What's interesting is, you'll see areas further west of that, now under the New Israelite gradient, that are still feudal in nature. (Particularly Texas) There's also Voodoo Mississippi to the south. The alligator flag belongs to Red River, which seems to be a hodgepodge of Arkansas, Texas and Louisiana. Note that it's the largest kingdom without a Church HQ in it. I think this generally indicates that while the South observes Non-Dom, it may not have as much to do with it. We may likely see a schism in the South--maybe this is what the East Heresy page might have talked about.