I was reading this wikipedia article on waxy corn and it states in the intro that

Until World War II, the main source of starch in the USA was tapioca but when Japan severed the supply lines of the States, they forced processors to turn to waxy maize.

I would have thought potatoes, or maybe sweet corn, but Tapioca seems oddly specific. I know that Cassava is popular in South America, but can anyone verify/explain this quote? I just can't imagine my great-grandparents wolfing down pudding at every meal, rather than potatoes. Or blow my mind, either way is fine.