Processed food has been around in many forms for a long time (pasta and bread are processed food). You're thinking of ultra-processed foods, which came later.
This was, however, the start of a radical change in food culture in the US. WWII introduced refrigerated food transport, improvements in canning, and developing frozen and shelf-stable meals. The result was 2-3 decades of Americans eating TV dinners and canned foods, as well as the rapid expansion of fast food restaurants. The growth of supermarkets and year-round produce then shrank the available variety of foods, and intensive ag practices reduced the nutritional quality of those foods.
Thank God for Julia Child. She single-handedly turned the tide away from an ocean of bland crap and back towards delicious home-cooked meals (for a small portion of Americans, anyway). It did not stem the tide against the rise in obesity, which began in the 70s, largely due to the explosive growth of cheap fast food and junk food, lobbying, and a lack of education around food and health.
This was, however, the start of a radical change in food culture in the US. WWII introduced refrigerated food transport, improvements in canning, and developing frozen and shelf-stable meals. The result was 2-3 decades of Americans eating TV dinners and canned foods, as well as the rapid expansion of fast food restaurants. The growth of supermarkets and year-round produce then shrank the available variety of foods, and intensive ag practices reduced the nutritional quality of those foods.
Thank God for Julia Child. She single-handedly turned the tide away from an ocean of bland crap and back towards delicious home-cooked meals (for a small portion of Americans, anyway). It did not stem the tide against the rise in obesity, which began in the 70s, largely due to the explosive growth of cheap fast food and junk food, lobbying, and a lack of education around food and health.