HR2 Disease in the New World

The New World suffered from infectious diseases at relatively higher rates and with greater mortality than did the Old World, but due to a couple of POD factors (e.g., continued survival of horses and arrival of Chinese ca. 1200 AD and subsequent indigenous response), disease took less of a toll on indigenous populations in [North America] than it did in OTL. Unfortunately for [South Americans], the above POD factors did not benefit them, and they succumbed to disease at the same rates as OTL.

It remains unclear how much overall resistance to infectious disease would have conferred to native [North Americans] because, although access to horses would have provided the natives some similar immune systems benefit to that provided to Europeans who lived among herd animals, the specific cocktail of Euro diseases was nasty: smallpox, bubonic plague, chickenpox, cholera, the common cold, diphtheria, influenza, malaria, measles, scarlet fever, sexually transmitted diseases, typhoid, typhus, tuberculosis, pertussis (whooping cough), etc.

Disease, population collapse, and their impacts in both Miskanaka and Anahuac
I had written above about contact with the Chinese starting in ~1200 AD and subsequent disease events that followed. Drawing from the chart above about Mexico,

With trade between Miskanaka and Anahuac came small pox, causing devastation among both peoples and effectively curtailing the Gold Road trade.

Miskanaka and Anahuac each experienced a similar (if less dramatic) population drops from ~1200 to ~1300, with population declines similar to those in Europe from the Black Death from multiple disease routes. Miskanaka adapted by using ritualistic cleansing and proto-inoculation rites, and Anahuac adopted more dramatic tactics (such as social isolation and extreme paranoia of outsiders in addition to inoculation rites), as it experienced harsher population losses. As of 1456, the populations of each nation stood at 6 million and 10 million respectively, about 2/3 of what each had been at their heights at ~1200 and about double what they were at their respective nadirs in the 1300s.

As both nations recovered, each entered into a distinct development phase. To the north, Miskanaka confined the Chinese to two major trading ports and began developing elaborate purity rites. They maintained ties with their eastern trading partners and eventually made contact with the Vinlanders over the next two centuries. To the south, the Anahuac militarized, developing arms and a bunker mentality. They pushed north to secure the entire Gulf of Aztlán and ceased trade with the Miskanaka.

In spite of their precautions, indigenous [Americans] still have relatively high disease mortality rates from foreign ailments, and they live with the constant looming spectre of death by disease in their children. Large families started early (marriage age <18 y/o is common) with many young children (>12 per couple on average) are a given as a result. Three and four generations commonly live together in extended family units. Young children are doted on from birth and are viewed as a source of joy up through about age 8, when they are expected to participate in the disease rites and start preparing for family life. To the extent possible in an iron age culture, civic measures to favor those couples who have passed on disease resistance in their children are made. Since neither germ theory nor genetics are anywhere close to being understood at this point, various reasons for why some family lines are "stronger" than others have been developed, mostly centering on fidelity to ritual, divine favor, excellence in one or more of the four paths, and so on. The practical upshot of all this is two societies that are relatively more resistant to European diseases than their neighbors and that harbor unique bugs of their own to which they are relatively resistant but cause harmful effects in Europeans (e.g., syphillis, but also others to be elaborated on in future lore).