The key document that secured women’s suffrage in 1920 in the United States was the Nineteenth Amendment to the Constitution. This amendment, ratified on August 18, 1920, legally granted women the right to vote after decades of activism and struggle. The suffrage movement gained momentum in the late 19th and early 20th centuries, fueled by organized campaigns, protests, and advocacy groups like the National American Woman Suffrage Association. Women fought against significant opposition, but their perseverance and growing influence in society ultimately led to this historic constitutional change. The amendment marked a significant milestone in the quest for gender equality in the U.S.