Norma, I have all of those but the Johnny-Come-Lately article. Thanks for adding another article to the mix!
Yes, pizza was nearly completely unknown outside of the culturally-tight enclaves of inner-cities until the late 1940s.
American GI's returning from WWII that were stationed in Southern Italy are often cited as the reason pizza exploded in the 1950s. From what I have read this is a very large reason, but not the full picture. Other articles also talk about the boom in the economy after WWII (also true) and that for the first time much more of the population had the means to travel overseas...and these people tried foods from foreign lands for the first time and by and large liked it, with Italy being one of the most popular travel destinations in those days for Americans (as it is now). Those people brought a hankerin' for pizza back from their travels.
It's amusing, and sad, that some of the mechanisms and changes which helped usher in the boom of pizzerias during the 1950's and 1960's immediately cheapened the product and began the downward slide of pizza into a cheaply constructed, commodity food of baneful quality (which is what nearly all "NY-Style" pizza, even in NYC, is these days...s*^t).
The bloom was definitely off the rose right off the bat.....the "synthetic cheese" versus the "real mozzarella" wars between American Cheese Makers and the Italians making fior-di-latte in the late 40's and early 50's being one example. --K