...100s of techniques for preservation were invented.
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The populaton grew even before electricity.
Look at the DIY food preservation vids from the Turkish areas. These folks often still are subsistence farming in areas with little or no power.
Fruit: Cover w/boiing water to blanch. drain. Add sugar (a moderate amount) and boiling water. Seal, cool, will last 1 year in cool storage.
Fruit and veg can be preserved with lacto-fermentaion. Can use just salt or add garlic and pickling spices. Will keep harvest-to-harvest if kept cool.
I’ve tried lacto-fermentation. Works well. Tomatoes with just salt tasted about as good as canned, but the cherry tomatoes became fizzy, which is an acquired taste. Fruits form a syrup with the above process. The meat relies on the fat, so just venison or just rabbit needs something added.
In ancient Europe, duck and chicken were preserved ala confit, which is cooked in fat and covered with a layer of fat which keeps out the air. Good for months at a time if kept cool.
Humans have been surviving winter in the Northern Hemisphere for eons and all we hear is how there are too many of us.
I’ve lived in the country for nearly 50 years and never saw a rat, just field mice. Cats or terriers help and I haven’t even seen a mouse this year since we had a bumper crop of acorns in our woods. And I experimented with those: not that difficult to extract the tannins and make them edible. High in protein. Pretty bland, but porridge of all types is also bland.
And no tubercular patient managed to populate the West. That took stamina and strength.
I think all the gardeners and hunters and farmers will have a more optimistic approach to preservation. Not everyone will survive. But we likely are not going back to the stone age everywhere and not FOREVER (!).
I figure if the voyagers survived the northern winters out in the bush, as did the native peoples, lots of present-day Americans will, as well.
Meat (needs fat): cut into small pieces, top jar with fattiest pieces. Place in bottom of deep cooking pot, on top of a folded towel. Keep pot covered and simmering 6-8 hours, replenishing with boiling water as needed. Can be done over an outdoor fire. The fat will cook out of the meat and join with the fat pieces at the top of the jar, acting as a seal. Will last a year if kept cool.
Keep cool in a dugout or natural root cellar purpose-built on the North side of a house/out-building or hill. Otherwise, you need sugar, salt, canning jars, garlic/spices.
Besides food preservation, there are DIY vids showing how poor people in remote areas today still utilize 18th/19th century techniques to produce machinery that works. Not for everyone, but can be done.
https://www.pbs.org/wgbh/americanexperience/films/plague/
The Forgotten Plague, a layout of Tuberculosis and how it defined many things, among them western expansion in America.
You started out your description with a comment about population.
A look at historical global population finds only one period of history when population declined. Not during war. Not during natural disaster.
Black plague. Yersenia Pestis. It never reached South America during the 1300s-1400s, if it had we would have been looking at a global population crash of 80% instead of 50% incl China and India.
But the key point of plague was population recovery. It simply did not happen. The calorie balance was badly damaged. It turns out Europe population did not return to 1340 (1348 plague arrived in England) levels until the early 1500s. Over 100 years.
And what did it? The potato. Columbus brought potatoes back to Europe from the New World in 1493. Potatoes are a solid calorie total per acre. Not much distance hauling to harvest them. Very long growing season in the context of “early potatoes” in July and then the main crop towards autumn, and yes, that reduced storage reqmts from 12 months to about 8 or 9.
The matto grasse in southwest Brazil gets 3 crops per year. THREE!! That country will never starve.