Which version of pizza are you talking about? Apple didn't technically invent the first smartphone, and yet it did create and popularize the smartphone as the world knows it today.
The US also didn't actually invent putting cooked beef between two slices of bread. It popularized and spread the hamburger globally. What the world came to know as a hamburger, came from the US.
Pizza, as with so many commercialized things, was popularized around the globe by the US, not by Italy. That's not something up for debate, it's not subtly the case, the US massively popularized pizza as the world knows it today. It wasn't the classic, bland Italian version of 'pizza' that stormed around the world, it was the amped up commercialized US approach to pizza: which involved an epic explosion of variation of every possible sort, delivered by chains. That's what rapidly spread pizza to every corner of the globe post WW2. The US created the modern pizza chain and spread it globally, using its vast economic reach and capital, introducing pizza to billions of people in the process. Pizza was popularized globally by the US in exactly the same way the US popularized hamburgers.