The Naples region in southern Italy is famous for its tomatoes. Spaghetti with tomato sauce was also commonly eaten. Immigrants from Naples to New York couldn't get tomatoes as delicious as those from Naples in New York, so they substituted tomato ketchup to make spaghetti. This delicious spaghetti spread throughout America. After the end of the war in 1945, the United States military occupation began under the supreme commander of the Allied Forces, Douglas MacArthur. At that time, Hotel New Grand became the lodgings for GHQ officers. Among the preserved food they brought with them was a large amount of spaghetti and tomato ketchup. American soldiers liked to eat spaghetti seasoned with tomato ketchup and salt and pepper. After the U.S. military returned home, Shigetada Irie, the second-generation executive chef after the war, saw a large amount of spaghetti left behind and improved upon it, creating tomato ketchup-flavored spaghetti. Stir-fry chopped garlic and onions until golden brown, add boiled tomatoes, fresh tomatoes, and tomato paste, and season with olive oil and bay leaves to make a sauce. When mixed with spaghetti, "Spaghetti Neapolitan" is completed. It's just like how Japanese sushi has turned into a ridiculous dish in other countries. Japanese people are well aware that the authentic pasta with tomato sauce eaten in Italy is definitely the most delicious.
It is hard to explain to Italians that tomato sauce after world war 2 was hard to acquire globally and that is why so many dishes around the world used ketchup as a substitute. there are even dishes in southeast asia and in north america that also use ketchup and italians are always horrified. after all, fresh tomato in their country is always available and cheap. italian cuisine is often about using few and fresh ingredients. cream substituting for cheese is also a global phenomenon that italians are traumatized by. since italians will always use the correct kinds of cheese, whereas other places in the world can't afford those expensive cheeses and will use cream and salt instead.