In this context, 1921 refers to the specific year when the legislation was enacted, which established the quota system limiting immigration to the United States.
Related terms
Roaring Twenties: A nickname given to the decade of the 1920s due to its social, artistic, and cultural dynamism.
Prohibition Era (1919-1933): A period during which alcohol production, sale, and distribution were prohibited by law in the United States.
Great Migration (1916-1970): The movement of millions of African Americans from rural areas in the South to urban areas in Northern cities during this time period.