But how did it get so big so fast in the United States? Post-war mid-century American history combined a number of key factors to create the perfect storm in which pizza would become arguably the most dominantly popular food in the U.S. for the next 70 years.
1. Production: A pizza parlor needs only two pieces of specialized equipment, a heavy stand mixer for the dough and an oven that can hold temperatures over 550F. A particularly handy person could even build an oven themselves. So long as you weren't trying to open a full-service restaurant with lots of seating and a varied menu, the only expensive piece of equipment you would need to acquire is that stand mixer.
2. Infrastructure: after World War II, the US government had a lot of surplus items they were selling cheap: jeeps, canteens, army boots... and huge Hobart stand mixers. The Hobart mixers were big enough to mix a battalion's bread, and they were going cheap. A vet could get a small business loan from the GI bill, buy himself a mixer, rent a small storefront, build an oven, and viola! He was in the restaurant business. Just like that. It's a restaurant that can make a lot of pizza efficiently, but it can't make much else. In this bare bones operation, a restauranteur had limited capacity for sit-down traffic and limited menu. And for many folks, that was just fine.
3. Portability: This may, in fact, be the most under-appreciated aspect of the dish. As pizza parlors spread from urban centers, owners realized there was a limit to the walk-in traffic they could expect. They knew from their urban experience many customers were taking the pizza home. How could they replicate that trade in the suburbs? By offering a new service: pizza delivered to the customer's house. And that was the real ticket right there. Delivery. There is no other food that holds up to travel and portability like pizza. It is the supreme delivery food item.
With third-party food delivery services coming into the market, and cloud based apps for them, that last point is important to note. Pizza is the supreme delivery food.

If those factors hadn't lined up the way they did...who knows what would've happened? Somewhere, there is an alternate universe in which hardly anybody eats pizza.
Sucks for those guys.