Which amendment, ratified in 1920, prohibited denying the vote in the United States based on sex?

The amendment ratified in 1920 that prohibited denying the vote based on sex was the Nineteenth Amendment.

The amendment states that the right of United States citizens to vote cannot be denied or abridged by the federal government or any state on account of sex. Congress proposed it in 1919, and Tennessee became the thirty-sixth state to ratify it on August 18, 1920, providing the approval then required. It was certified on August 26.

The amendment followed decades of activism by women’s suffrage organizations and leaders including Susan B. Anthony, Elizabeth Cady Stanton, Ida B. Wells, and Carrie Chapman Catt. The movement used petitions, public speeches, marches, civil disobedience, and state-level campaigns to press for voting rights.

Ratification did not immediately guarantee equal access to the ballot for all women. In practice, many Black women and other women of color continued to face poll taxes, literacy tests, intimidation, discriminatory registration systems, and other barriers. Later civil-rights laws addressed many of those obstacles.