How did deregulation of business take place in the 1920s?

Deregulation is the process of removing or reducing state regulations, typically in the economic sphere. It is the repeal of governmental regulation of the economy. It became common in advanced industrial economies in the 1970s and 1980s, as a result of new trends in economic thinking about the inefficiencies of government regulation, and the risk that regulatory agencies would be controlled by the regulated industry to its benefit, and thereby hurt consumers and the wider economy.
Economic regulations were promoted during the Gilded Age, in which progressive reforms were touted as necessary to limit externalitieslike corporate abuse, unsafe child labor, monopolization, pollution, and to mitigate boom and bust cycles. Around the late 1970s, such reforms were deemed as burdensome on economic growth and many politicians espousing neoliberalism started promoting deregulation.