1920 amendment mandating women’s suffrage
Source (Wikipedia): Nineteenth Amendment to the United States Constitution

The Nineteenth Amendment to the United States Constitution prohibits the United States and its states from denying the right to vote to citizens of the United States on the basis of sex, in effect recognizing the right of women to vote. The amendment was the culmination of a decades-long movement for women’s suffrage in the United States, at both the state and national levels, and was part of the worldwide movement towards women’s suffrage and part of the wider women’s rights movement. The first women’s suffrage amendment was introduced in Congress in 1878. However, a suffrage amendment did not pass the House of Representatives until May 21, 1919, which was quickly followed by the Senate, on June 4, 1919. It was then submitted to the states for ratification, achieving the requisite 36 ratifications to secure adoption, and thereby went into effect, on August 18, 1920. The Nineteenth Amendment’s adoption was certified on August 26, 1920.