Why are the 1920s known as the roaring twenties

The 1920s in the United States, called “roaring” because of the exuberant, freewheeling popular culture of the decade.

Explanation:

The Roaring Twenties was a time when many people defied Prohibition, indulged in new styles of dancing and dressing, and rejected many traditional moral standards. (See flappers and Jazz Age.)

Laroi

in all honesty, it really hasn't. except that hitler killed himself.

i would go with the last one