In the late 1800s and the early 1900s, Neapolitan immigrants came to the USA in search of a better life. Shortly after, in 1943, their descendants, Ike Sewell and Ric Riccardo had opened Pizzeria Uno in Chicago, serving a new variety of pizza in a deeper dish, with inverted layers of cheese, meat, and tomatoes, and a crunchy crust.
No longer an immigrant tradition, Chicago-style deep dish pizza is now one of Chicago's cultural and culinary icons. The dish is not just popular in Chicago, but all over the world, and its popularity is evident in the fact that there is even a National Deep Dish Pizza Day, celebrated every year on April 5.