>>17937306
>Our δ18O records provide valuable information regarding climate variations in late Holocene central Mexico. For example, El Niño–Southern Oscillation decoupled from the Intertropical Convergence Zone (ITCZ) mainly drove late Holocene climate, particularly between 900 and 1550 CE, causing a dry Medieval Climate Anomaly and a wet early Little Ice Age. Most interesting, our results indicate that the decline of Teotihuacan could be partially attributed to seventh-century droughts induced by a coupling of pronounced El Niño and reduced solar output (i.e., a more southern location of the ITCZ). Also, these droughts seem to have caused a corresponding migration from the west into the Basin of Mexico

>>17937306
> Our δ18O records provide valuable information regarding climate variations in late Holocene central Mexico. For example, El Niño–Southern Oscillation decoupled from the Intertropical Convergence Zone (ITCZ) mainly drove late Holocene climate, particularly between 900 and 1550 CE, causing a dry Medieval Climate Anomaly and a wet early Little Ice Age. Most interesting, our results indicate that the decline of Teotihuacan could be partially attributed to seventh-century droughts induced by a coupling of pronounced El Niño and reduced solar output (i.e., a more southern location of the ITCZ). Also, these droughts seem to have caused a corresponding migration from the west into the Basin of Mexico

Even a year long winter would make any sort of society beyond small scale migratory pastoralism impossible, nevermind a continent wide society built on feudalism functioning off high medieval age technology (minus stuff like gunpowder of course because guns ruin le fantasy). A multi-year winter hitting would cause their entire society to collapse as starving peasants bust open the granaries, domesticated animals die off as feed and fuel for heat runs out and starving royalty eat their horses, and towns crumble under a cascade of snow and disease as waste collects and piles up unable to be carried way by frozen rivers and ice over cesspools.