Pizza in the United States

Numerous regional variations of pizza in the United States have been developed, with many bearing only a casual resemblance to the Italian original. Pizza became most popular in America after soldiers stationed in Italy returned from World War II. 
During the latter half of the 20th century, pizza became an iconic dish of considerable popularity in the United States. In some parts of North America, the slang term "za" is also used for pizza. The thickness of the crust depends on what the consumer prefers; both thick and thin crust are popular. Often, foods such as barbecued chicken and bacon cheeseburgers are used to create new types of pizza.
Pizza is a popular fast-food item. The United States pizza restaurant industry is worth $37 billion, and has an organized industry association. Pizza is normally eaten hot (typically at lunch or dinner), but is sometimes eaten as cold leftovers, even for breakfast.
History.
The first pizzeria in the U.S. was opened in New York City's Little Italy in 1905. Common toppings for pizza in the United States include anchovies, ground beef, chicken, ham, mushrooms, olives, onions, peppers, pepperoni, pineapple, salami, sausage, spinach, steak, and tomatoes. 
Distinct regional types developed in the 20th century, including Buffalo, California, Chicago, Detroit, Greek, New Haven, New York, and St. Louis styles. These regional variations include deep-dish, stuffed, pockets, turnovers, rolled, and pizza-on-a-stick, each with seemingly limitless combinations of sauce and toppings.
Thirteen percent of the United States population consumes pizza on any given day. Pizza chains such as Domino's Pizza, Pizza Hut, and Papa John's, pizzas from take and bake pizzerias, and chilled or frozen pizzas from supermarkets make pizza readily available nationwide.
Ingredients.
American pizza often has vegetable oil or shortening mixed into the dough; this is not as common in Italian recipes (for example, the pizza dough recipe in the influential Italian cookbook "Il cucchiaio d'argento" does not use oil). This can range from a small amount in relatively lean doughs, such as New York style, to a very large amount in some recipes for Chicago-style deep-dish dough. In addition, American pizza (at least thin-crust) is often made with a very high-gluten flour (often 13–14% protein content) of the type also used to make bagels; this type of flour allows the dough to be stretched rather thinly without tearing, similar to strudel or phyllo.
In some pizza recipes, the tomato sauce is omitted (termed white pizza), or replaced with another sauce (usually garlic butter, but sauces can also be made with spinach or onions).