The Great Depression was a period of economic and social upheaval in the United States that, by most accounts, started on Black Thursday, 24 October 1929, when the New York Stock Exchange traded over 12 million shares. Following a brief rally, the market experienced its largest drop in aggregate share price ever the following Tuesday, 29 October. During this market upheaval, many investors were wiped out -- made financially insolvent -- overnight, and quite a number of them suicided, often by jumping from the high offices where they worked. Most historians consider these events the end of the Roaring 20's, a period of exuberence and optimism. Over the next decade, banks failed, standards of living plunged, and joblessness soared. President Franklin Roosevelt and the Congress enacted numerous programs to serve as social safety nets, and to stimulate the economy, with varying degrees of success. Many of these changes, such as a powerful central bank, persisted for decades after their enactment.
The misery of the Great Depression was the backdrop for James T. Kirk's visit to the early 20th century. An overdose of cordrazine had rendered Leonard H. McCoy temporarily insane, and McCoy had fled through the Guardian of Forever -- altering the past in a way that eliminated the Federation from the timeline. Pursuing him, Kirk and Spock also journeyed to Earth's past, there encountering social worker Edith Keeler. Through Keeler, they were eventually reunited with McCoy. Kirk also fell in love with the young woman -- tragically, since she was fated to die. (TOS: "The City on the Edge of Forever")