So many things came together to create the global expression, aside from tax, tariff, & banking policy there were after effect of the Great War - the economics of the Versailles Treaty & all that, the hole left by the conversion of the Imperial Russian economy to the Communist Soviet, collapse of Chinas economy during the warlord era... Beyond all that was a volatility created by a number of significant changes in technology. Mature industries like the railroads, coal energy. newsprint or telegraph communication continue to slow their growth opening fewer high paying jobs and becoming less attractive for investment. New technologies have a high failure rate in startups creating volatility in both employment and investment. While new industries pay a premium for the skills the need labor/management without the experience starts at a lower wage than they would have in the maturing industries. The larger number of mature/aging industries and larger number of start ups, early growth technologies concentrated in a decade, a 'crossover point' as it were, the more volatile and disrupted the markets, investment, employment, ect.. become. Perhaps the largest change in the 1920s-30s was the turnover from the rural agriculture to the urban industrial. At the start of the 1920s the majority of the US population was still rural agricultural. The conversion had been a ongoing thing that had been relatively slow but accelerating. In the early 20th Century this accelerated & the interwar years saw a relatively large and rapid turnover. This trend was not confined to the US. Germany was undergoing the same transition, the former Austrian Hungarian states were close to the tipping point in this, France and Britain had crossed it earlier & were trying to asorb the remnant surplus of labor from their agricultural sectors.
Changing US tax policy has a effect, but its a part of a larger whole.