...by people who don’t know where what they think of as “Italian pizza” actually comes from. Look up “pizza effect.”
Pizza existed before Italian migration to North America was even a thing. It gained tomatoes when they became more readily available and better known in the early XIX century, and that's about it. The explosion in Italian migration happened later, by then most of the traditional pizzas had long been codified.
WRT pizza, it's clearly false. Pizza was a thing in Italy before World War II and it spread through Europe from Italy, not from the USA. You can trace the history of many pizzerias in Italy back far further than the "pizza effect" would have you believe, so you can easily de-bunk it by going to the web site of a pizza place in Napoli.
Amusingly, however, while it’s influence on the food itself is at the very least debatable, the influence of the US on how pizza is consumed is in fact very real: the fact that Italians nowadays drink beer with their pizza is something they learned from American GIs in WWII who brought the practice over from home.
Before that time, there was no overlap between Italians who drank beer (Northerners) and Italians who ate pizza (Southerners). Thanks the American soldiers Southerners learned to drink beer and Northerners learned about pizza.
Pizza margherita existed in the I̶X̶X̶ XIX century already in its modern form.
