Or, the automobile, the industrial revolution, and a booming population through agriculture and medical improvements led to economic prosperity, despite a deadly plague.
It's a pretty hard case to make that a disease which disproportionately killed health 20-30 year-olds led to mass prosperity.
Given all the advancements which were happening in the early 20th century, I'm inclined to say that prosperity happened in SPITE of WWI and the Spanish Flu. Who knows where we would be, had we avoided two huge human catastrophes.