On Aug. 18, 1920, a 24-year-old state legislator from East Tennessee walked into the Tennessee House chamber wearing a red rose on his lapel. Red meant no. The chamber was deadlocked 48-48. The 19th Amendment needed one more state, and Tennessee was the last realistic option.

Harry Burn had a letter in his pocket from his mother, Febb Burn, a college-educated widow who read three newspapers a day. On the final page of seven, she got to the point: “Don’t forget to be a good boy, and help Mrs. Catt put the ‘rat’ in ratification.” He changed his vote. The amendment passed 49-47. The most consequential roll call in the 72-year history of the suffrage movement came down to a mother’s letter.