No pressure canners. No refrigerators. No money to buy expensive canned (tinned) food.
That was the situation for many pioneer farmwives. Very little cash was available to these families, especially as many settlers saved to put up a multi-room home and buy farming equipment. To put away their cash for these, women resorted to vinegar. They created what seems today to be odd pickles.
Root vegetables like potatoes (which were served at nearly every meal) could be stored in underground cellars. Other vegetables were needed in the winter also, so what couldn't be dried was pickled.
Fish and meat along with vegetables ilke green beans and fruits like peaches would be pickled. Busy women scrounged the areas around their farms to supplement what they could put up for the winter. Apples and gooseberries were examples of what might be found and pickled.
In researching about this, the recipe that most surprised me used green tomatoes. From The Woman Suffrage Cookbook, this recipe dates back to 1886 in print. It was undoubtedly used before that.