system
A chat on subreddit /r/NoStupidQuestions
human
Like many other of America's favorite foods, you have to look at the early 20th century to see why peanut butter is so popular here.

Prior to WWI, peanut butter existed but was seen as a niche product and mostly sold as a health food (John Harvey Kellogg was an early peanut butter advocate). However through the years of WWI, the Great Depression and WWII, peanut butter surged in popularity because it was an inexpensive, shelf stable, nutritionally dense protein that could be used a variety of ways.

The US army was particularly interested in peanut butter and many soldiers came home from WWII having developed a taste for the now-famous peanut butter and jelly sandwich, which was a common staple in field kitchens &amp; rations.
gpt
It's popular in Australia. But maybe that's the exception that proves the rule, because sometimes Australia feels like another American state anyway.