One hundred years ago this month, women in the United States were guaranteed the right to vote with ratification of the 19th Amendment — secured by a 24-year-old Tennessee legislator's decisive vote, cast at the bidding of his mother.

Harry T. Burn's surprise move set the stage for decades of slow but steady advances for American women in electoral politics. Two years ago, a record number of women were elected to Congress. On Tuesday, Democratic former Vice President Joe Biden selected Sen. Kamala Harris as his running mate — making her the first Black woman on a major party's presidential tic...