The 1920s (pronounced "nineteen-twenties" often shortened to the "'20s" or the "Twenties") was a decade that began on January 1, 1920, and ended on December 31, 1929. Primarily known for the economic boom that occurred in the Western World following the end of World War I (1914–1918), the decade is frequently referred to as the "Roaring Twenties" or the "Jazz Age" in America and Western Europe, and the "Golden Twenties" in Germany, while French speakers refer to the period as the "Années folles" ('crazy years') to emphasize the decade's social, artistic, and cultural dynamism.

The devastating Wall Street crash in October 1929 is generally viewed as a harbinger of the end of 1920s prosperity in North America and Europe. In the Soviet Union, the New Economic Policy was created by the Bolsheviks in 1921, to be replaced by the first five-year plan in 1928. The 1920s saw the rise of radical political movements, with the Red Army triumphing against White movement forces in the Russian Civil War, and the emergence of far-right political movements in Europe. In 1922, the fascist leader Benito Mussolini seized power in Italy. Other dictators that emerged included Józef Piłsudski in Poland, and Peter and Alexander Karađorđević in Yugoslavia. First-wave feminism made advances, with women gaining the right to vote in the United States (1920), Albania (1920), Ireland (1921), and with suffrage being expanded in Britain to all women over 21 years old (1928).

In Turkey, nationalist forces defeated Greece, France, Armenia, and Britain in the Turkish War of Independence, leading to the Treaty of Lausanne (1923), a treaty more favorable to Turkey than the earlier proposed Treaty of Sèvres. The war also led to the abolition of the Ottoman Caliphate.