The right answer is The economy grew quickly.
The ten years between 1919 and the onset of the Great Depression at the end of 1929 encompassed a period of unprecedented economic prosperity and cultural experimentation as well as political conservatism and religious fundamentalism. The large, growing middle class of Americans who had formed an important segment of the progressive political coalition was now absorbed instead into the prosperous “New Era” created by advances in communications, transportation, business organization, and the spread of mass consumerism.