This is the fifth post in our series on what social science can tell us about the Women’s March on Washington. Here are the first, second, third and fourth. — TMC editors

The Women’s March on Washington was likely the largest single-day demonstration in recorded U.S. history. The only potential competitors were the Vietnam War Moratorium days in 1969 and 1970, which boasted millions of participants worldwide (and up to 1 million in the United States). The first Earth Day in 1970, which some claim had between 10 million and 20 million participants, did involve some demonstrations, but much of the activity involved local educational workshops and science fairs held at schools. And in February 2003, an estimated 10 million people demonstrated worldwide in opposition to the U.S. invasion of Iraq, with around 1 million of those marching in the United States.