In the Great Gatsby, What event percede the "roaring twenties", and perhaps even contirbute to it?

WWI preceded the "roaring twenties," contributing to the happiness, freedom, and pride of the American people. But Fitzgerald also notes the division of social classes and the disparities between the rich and poor.

We are also introduced to "new" money, which in the 1920's was often accumulated thought illegal means. Prohibition officially began on January 16th, 1920, and bootlegging made many people rich. Note; old money rarely mixed with new money. Thus, we have another unconquerable chasm between Gastby and the Buchanan’s (namely Daisy).