Pizza was taken to the United States by Italian immigrants in the late nineteenth century and first appeared in areas where they concentrated. The country’s first pizzeria, Lombardi’s, opened in New York City in 1905. Following World War II, veterans returning from the Italian Campaign, who were introduced to Italy’s native cuisine, proved a ready market for pizza in particular.
Thirteen percent of the United States population consumes pizza on any given day.
https://en.wikipedia.org/wiki/Pizza
I think that number is a little low.