the most important reason for the economic boom was the Technological progress that the US had, that also includes Fordism. I will start speaking of Henry Ford and how he revolutionized the automobile industry. Then I will follow with all the new inventions that the US had. Then I will conclude with why I think this reason is above all others.
Henry Ford revolutionized car manufacturing and started the second industry revolution in Detroit, Michigan. He did this through the assembly line technique. Unskilled and low skilled workers could learn how to assembly a car in a short period of time. Ford then concentrated on building a lot of cars; he only built black Model T cars. Also since he was incredibly rich, now he could pay his workers a high amount of money, 5$ US a month, a large amount of money for an industrial worker. As a result of the payment the workers were expected not to join trade unions and follow the strict company rules.
By 1926 Ford was building a Model T car every 10 seconds, by 1927 15 million Ts were built. By 1929 the auto manufacturing industry employed 7% of the industrial workers in the US.
The US also helped the car companies by passing the federal highways act of 1921; they built an average of 10,000 miles of road a year. Roads grew from 350,000 miles in 1919 to 662,000 on 1929.
The US had great inventors such as Thomas Edison who said 'Genius is 10% inspiration, 90% perspiration'. The States had the light bulb, sewing machine, phonograph and telephone, all as a result of American ingenuity.
To conclude I think that the spirit in those days and also the luck of getting so many technological advancements on that decade influenced greatly...