War and the economic depression caused many to turn to God and others to turn away from him. Major efforts were made to spread christianity in the heathen nations and communism emerged as a force opposing christianity. Evolution challenged Creationism.
Religion and Religious Faith still strong but challenged by Evolutionists
The church due to its legal separation from the state was not formally involved in politics, but took a strong interest in issues like the family, marriage and divorce, prohibition of alcohol, employer-employee relationships, crime and other social issues.
As the automobile and buses increased the mobility of country people then small local churches closed down and congregations consolidated in larger towns within commuting distance. This required less clergy and created efficiencies in maintainance and running costs for buildings. Once the depression hit and donations to churches decreased then church and missionary budgets were curtailed.
The Lambeth proposals, which were promulgated by a conference of Anglican and Episcopal bishops from all over the world in August, 1920,
provided, in brief, for a reunion of the churches on the basis that priests of the Roman and Greek Catholic Churches would be accepted as priests of the Anglican
Church if their own communions would reciprocate, while it was asked of the Protestant Churches that they would allow their ministers to submit to reordination
by Anglican or Episcopal bishops. Meetings were held during the 1920's to try and further the cause, but acceptance of ordination authority
was a major stumbling block.
New scientific discoveries and theories flourished causing doubt on the biblical version of events. Educational institutions promoted scientific learning based on facts causing some to label them as "incubators of agnosticism".
Numerous books were published in defence of religion including one by A.S. Eddington, a physicist, who pointed out that science does not solve any of the ultimate problems. Harvey Wickham took aim at those with a limited knowledge of science who were heaping scorn on traditional beliefs and morality.
At the same time as representatives of the Northern Presbyterian and Methodist churches were meeting to investigate the possibility of amalgamation, meetings were also taking place between Catholics, Protestants and Jews seeking common ground and looking to reduce religious bigotry and intolerance at the National Conference of Jews and Christians in New York.
In a stunt to create publicity for the small town of Dayton, Tennessee, a court case that became known as the Scopes Monkey Trial, took place in 1925 in which a high school teacher, John Scopes, was accused of violating Tennessee's Butler Act, which made it unlawful to teach human evolution in any state-funded school.
Scopes was charged with having taught from the chapter on evolution in a textbook to an April 24, 1925, high-school class in violation of the Butler Act and nominally arrested
William Jennings Bryan, three-time presidential candidate, argued for the prosecution, while Clarence Darrow, the famed defense attorney, spoke for Scopes. The trial publicized the Fundamentalist–Modernist Controversy, which set Modernists, who said evolution was not inconsistent with religion, against Fundamentalists, who said the word of God as revealed in the Bible took priority over so called "modern science".
Scopes was found guilty and fined $100, but the verdict was overturned on a technicality because Tennessee judges could not at that time set fines above $50, and the Butler Act specified a minimum fine of $100.
Wikipedia has a detailed account of the trial for those who want more information.