Prohibition developed as an unstoppable reform during the war, but Wilson played only a minor role in its passage. After decades of advocacy, in 1917 temperance groups such as the Woman's Christian Temperance Union and the Anti-Saloon League convinced both houses of Congress to pass a constitutional amendment imposing nationwide Prohibition. The amendment was ratified by the states in 1919, becoming the Eighteenth Amendment. In October 1919, Wilson vetoed the Volstead Act, legislation designed to enforce Prohibition, but his veto was overridden by Congress. Prohibition began on January 16, 1920; the manufacture, importation, sale, and transport of alcohol were prohibited, except in specific cases, such as wine used for religious purposes.