During 16th century the word pizza (from greek πιττα (pitta) meaning 'focaccia') appeared to describe a flat bread sold as street food.Until the 17th century was topped with oil and erbs or garlic, later other toppings were added like olive oil, lard, tomatoes, goats' milk cheese, anchovies. It was well described by Alexandre Dumas after a trip to Napoli in his Le corricolo (Éd.1846) .

Pizza margherita was probably created in 1889 adding mozzarella cheese as a topping, but it was not diffused since mozzarella was expensive and rare.

It was only after the war that pizza become ubiquitous in Italy, Ancel Keys was the researcher who associated the traditional Mediterranean diet with a low risk of CHD, attempted to but pizza in Rome in the '50 but it wasn't available anywhere, he was told that only neapolitans eat pizza.

It was only during the '60 that pizza became ubiquitous in Italy whan Luigi Giordano from Tramonti began mass production of mozzarella cheese in northern Italy.

https://angeloforgione.com/2022/03/16/inesattezze_pizza_pomodoro_mozzarella/