Americans love pizza. In fact, we spend $37 billion a year on the sauce-and-cheese-topped flatbread, accounting for a third of the global market, according to the USDA.

More than 40 million Americans eat pizza on any given day, and today, one in six males between the ages of 2 and 39 will eat pizza for breakfast, lunch or dinner.

Although we didn't invent pizza, Americans consume more of it than any other country.

Take a look at how this popular pie evolved from an inexpensive Italian food in the 1700s to a staple of the American diet.

A slice of history

Flatbreads with toppings aren't unique to Italy, but pizza can trace its roots back to Naples, where flatbreads topped with tomatoes, cheese and anchovies first became popular in the 18th century.

Frequently sold by street vendors, these early pizzas were affordable and could be consumed quickly, making them an ideal food.

In 1861, Italy unified, and when King Umberto I and Queen Margherita visited Naples, they dined on pizza. According to legend, the queen’s favorite pizza was the simple pie topped with cheese, tomatoes and basil, so pizza Margherita was named after her.

Although other cultures ate foods similar to pizza, it wasn't until the 1940s that pizza would become well-known outside of Italy.

As Italian immigrants made their home in the New World, they began replicating pizza in American cities, and the first documented U.S. pizzeria, G. Lombardi's, officially opened in New York in 1905.

After World War II, as more Italian-Americans migrated into cities and suburbs, pizza became increasingly popular. It was seen not as an ethnic food, but as something fast and inexpensive, and "American pizza" quickly spread to the rest of the world.

"Like blue jeans and rock and roll, the rest of the world, including the Italians, picked up on pizza just because it was American," author John Mariani writes in "How Italian Food Conquered the World."

But just because pizza has strong Italian roots and gained mass appeal in America doesn't mean it hasn't adapted to local tastes. Take a look at the infographic below to see how various countries eat their pie.