I don't get what you mean by saying "American style pizza".
Slices of pizza?
Or pepperoni or pineapple on top of it...? These last "inventions" no, definitely they were not Italian.
I had slices of pizza in bakeries in Milan when I was a kid/adolescent 50/55 years ago, and when my parents grew up up in Naples they had the same 80/90 years ago...of course it was only with tomato sauce and mozzarella.
Yes, now in Italy you find many places/bakeries which sell slices of different kind of pizza especially in tourist areas, but they still have an "Italian" (better!) twist with the same concept, and it is not an American influence.
Also gelato parlors when I grew up there had only a bunch of flavors and now you can choose among 20/25 of them, but that's an "evolution" due to the general idea of consumerism. Yes, this last is an American influence for sure!