Largest protests in American history

Constitutionally protected under the First Amendment, the right to assemble and protest was enshrined into the constitution under the clause, "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."

Widespread mass protest became a distinct characteristic of 20th century American civic engagement, with each of the top ten attended protests occurring since 1963.

In 1995, the National Park Service estimated 400,000 people attended the Million Man March in Washington, D.C., the official count for the event. The organizers said more than a million people turned out, and they threatened to sue the Park Service unless it revised its estimate. Congress, in response, barred the agency from producing any more crowd estimates.

Since then, official crowd estimates for organized political protests, demonstrations, and marches have relied on an amalgam of police data, organizer estimates, the research of crowd scientists, and journalists.

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