Golden Age of Freethought
The Golden Age of Freethought describes the 19th century United States socio-political movement which promoted freethought/atheism/agnosticism. The period from 1875 to 1914 is referred to as "the high-water mark of freethought as an influential movement in American society".
Politically, the atheist movement has leaned left in its politics (See: Secular left and Atheism and politics). Secular leftist utopianism and its exalted view of human nature did not line up with the horrors of the World War I. The Golden Age of Freethought ended at the start of World War I. In addition, atheism is negatively correlated with economic/political instability.
The Christian view of the fall of man better explained the horrors of WWI and WWII. Furthermore, Christian apologist point out that atheistic evolutionism contributed to the start of WWI (See: World War I and Darwinism). See also: Evolutionary racism and Nazi Germany.
The Cold War between the United States and the Soviet Union further chilled Americans receptiveness to atheism.
Susan Jacoby on the Golden Age of Freethought
Susan Jacoby wrote in her book Freethinkers: A History of American Secularism about the Golden Age of Freethought:
|“|| To describe the last quarter of the nineteenth and the first decade of the twentieth centuries as a golden age of freethought is to suggest not that a majority of Americans were persuaded by rationalist or antireligious arguments but that those arguments reached a much broader public than they ever had in the past. Unlike eighteenth-century deists, nearly all of whom identified with Jeffersonian democracy, American freethinkers of the late nineteenth century were anything but unified in their political views, which ran the gamut from anarchism to Spencerian conservatism. Freethinkers might be Democrats, rock-ribbed Republicans, or, on occasion, socialists with either a capital or a small s.
The one political concern that did unite all freethinkers was their support for absolute separation of church and state, which translated into opposition to any tax support of religious institutions-especially parochial schools...
Freethought periodicals, which proliferated after the Civil War, were important sources of communication within the freethinking community...
But the freethought lecture circuit--not the press--was the chief mode of communication between committed agnostics and a larger public that was interested in but did not define itself by religious skepticism. Americans flocked to lectures in every area of the country--whether in great cities where well-off inhabitants could afford to pay the munificent sum of one dollar for a ticket to a lecture by the famous [Robert Green] Ingersoll (scalpers in New York City, the newspapers reported disapprovingly, got up to two dollars) or in towns like Dowagiac, where a citizen might spend a nickel to hear a traveling lecturer at the Universalist Church, the established venue for heretical talks. General circulation newspapers treated the talks--especially the more controversial ones--as legitimate news events. Ingersoll, Stanton, and Anthony made headlines and sold newspapers wherever they went. 
Charles Louis Richter on the ending of the Golden Age of Freethought
Charles Louis Richter declared in his interview with the International Society for Historians of Atheism, Secularism, and Humanism (ISHASH) about America and atheism:
|“||The turn of the century ended the golden age of nineteenth century freethought with two events: the death of Robert Ingersoll in 1899, and the assassination of President William McKinley in 1901. The lack of a widely popular voice for irreligion, combined with the murder of the president by an anarchist, led to a backlash against not only anarchism but also atheism. From that point, Americans tended to see irreligion in terms of whatever ostensibly foreign ideology seemed most threatening. So for the rest of the century, we see atheism and atheists associated with anarchism, fascism, socialism, and of course Soviet-style communism. By the late seventies, secular humanism became the buzzword for a whole suite of threats not only to religion, but to Americanism. It’s important to note that this phenomenon is not limited to the political or religious right; liberals also framed irreligion as un-American.||”|