A sausage pizza sits on a table at Pizzeria Uno in Chicago, Jan. 20, 2010.
As Italian populations grew in U.S. cities, local entrepreneurs added their own unique twists to pizza. In New Haven, Conn., Frank Pepe opened a business in 1925 selling thin-crust “apizza” in two varieties—one with anchovies, one without (and neither had mozzarella cheese originally). Chicago deep dish pizza, meanwhile, can be traced back to 1943, when the restaurant that came to be known as Pizzeria Uno opened.