This International Women’s Day—celebrated every year on March 8— the world will pause to recognize the roughly 50 percent of the population who identify as women. But though the holiday has been co-opted by celebrities and brands, its roots are far more radical than you might imagine. More than a century ago, the holiday was created by socialist movement leaders impatient for equality for women.

In 1909, the United States labor movement and the push for women’s suffrage were both gaining steam. Russian refugee, labor organizer, and journalist Theresa Malkiel served on the women’s committee of the Socialist Party of America. Envisioning a more active role for women within the movement, she declared