America’s collective wealth more than doubled in a decade when change was the only constant. Mass communication and cheap transportation let us listen to the same music, buy the same goods and adopt a relatively common culture. Babe Ruth hit 60 home runs yet Mickey Mouse became the most well-known Yankee in the world. On the flipside, Jazz Age hypocrisy outlawed booze with the 18th Amendment and supported the rise of organized crime and, eventually, stock-car racing. As the decade ended, Adolf Hitler and Benito Mussolini cast a menacing shadow over Europe as America inched toward crushing financial disaster.