(Bonus) In the history of the 20th century, the interwar period lasted from 11 November 1918 to 1 September 1939 (20 years, 9 months, 21 days), the end of the First World War to the beginning of the Second World War. The interwar period was relatively short, yet featured many significant social, political, and economic changes throughout the world. Petroleum-based energy production and associated mechanisation led to the prosperous Roaring Twenties, a time of both social mobility and economic mobility for the middle class. Automobiles, electric lighting, radio, and more became common among populations in the developed world. The indulgences of the era subsequently were followed by the Great Depression, an unprecedented worldwide economic downturn that severely damaged many of the world's largest economies.