Anti-authoritarian and intellectually liberating historical eras had existed many times in history, notably in eighteenth century France.
But the period roughly from 1875 to 1914 is referred to by at least one contemporary writer as "the high-water mark of freethought as an influential movement in American society".
[1] It began around 1856 and lasted at least through the end of the century; author Susan Jacoby places the end of the Golden Age at the start of World War I. Freethought is a philosophical position that holds that ideas and opinions should be based on science and reason, and not restricted by authority, tradition, or religion.
The late nineteenth century American Golden Age was encouraged by the lectures of the extremely popular agnostic orator Robert Green Ingersoll, the popularization of Charles Darwin's On the Origin of Species, the push for women's suffrage, and other political, scientific, and social trends that clashed with religious orthodoxy and caused people to question the traditional ideas about the world that they encountered in received opinion.
Ingersoll, a lawyer, an orator and a Civil War veteran, is famous for his skeptical approaches to popular religious beliefs.