In March of 1907, Congress passed the Expatriation Act, which decreed, among other things, that U.S. women who married non-citizens were no longer Americans. If their husband later became a naturalized citizen, they could go through the naturalization process to regain citizenship.

But none of these rules applied to American men when they chose a spouse.

"It's as though she walks under his umbrella. He puts his arm around her and poof! she's a citizen," says Linda Kerber, a professor who teaches gender and legal history at the University of Iowa. "She has had the good sense to come out from these monarchies and opt for an American. She's a sensible woman, we adore her."

"Whereas an American-born woman who marries a foreign man, oh my goodness, she is disloyal," Kerber said.

When Mackenzie v. Hare — a case challenging the expatriation act that involved a woman married to a British citizen — reached the Supreme Court in 1915, the justices upheld the law, arguing that the women chose to marry knowing this was a consequence so they weren't being forced to expatriate. Then World War I began and hundreds of women found themselves affected by the law. ...