[Narrator:] "The Birth of a Nation" sparked a revival of the Ku Klux Klan in the 1920s.

The Klan's ideology of white supremacy

and what they called "100% Americanism"

resonated across the country.

[Mark Potok, Southern Poverty Law Center:] The Klan of the 1920s was not a rural Klan,

which the Klan of Reconstruction had primarily been.

The Klan of the 1920s was very big in surprising places,

places like Denver,

like Portland, Detroit,

which had huge waves of immigration

both of Catholics from Europe

and of African Americans coming from the South.

[Narrator:] In 1925, 50,000 klansmen and women gathered in Washington

in a vivid display of their numbers.

Four million Americans claimed Klan membership.

[Patsy Sims, Author:] That particular klan also became very, very powerful politically.

They elected at least 10 governors,

and there were all sorts of public officials

who were elected by power of the Klan.

[David Cunningham, Author, Klansville, U.S.A.:] The Klan has a great rise

in terms of membership through the first half of the 1920s,

and it has an equally spectacular fall.

There were a number of exposés of what the Klan was doing

in terms of its violent underside.

When you throw scandals in that really embarrass the leaders,

that kind of publicity really eroded its credibility.