A group protesting "modernist" tendencies in the churches circulated a 12-volume publication called The Fundamentals (1909-12), in which five points of doctrine were set forth as fundamental: the Virgin birth, the physical resurrection of Jesus, the infallibility of the Scriptures, the substitutional atonement, and the physical second coming of Christ. The debate between fundamentalists and modernists was most acute among the Baptists and the Presbyterians but also arose within other denominations. In a highly publicized case, the so-called Monkey Trial (1925), the fundamentalist leader William Jennings Bryan won Tennessee's case against J. T. Scopes, for teaching evolution in the public schools (see Scopes trial). Other attempts, however, by fundamentalists in the 1920s to rid the churches of modernism and the schools of evolution failed.

By the 1930s many fundamentalists began to withdraw into independent churches and splinter denominations, and fundamentalism became identified in the public mind with anti-intellectualism and extremism. Many fundamentalists rejected this image, and a movement was begun in the late 1940s to present their position in both a more scholarly and popular way. This movement, known as neoevangelicalism (or, more simply, evangelicalism), sought a wider following from the major denominations through its various schools, youth programs, publications, and radio broadcasts. The separatists saw these efforts as compromising fundamentalist views and sought to disassociate themselves from these religious institutions and such well-known evangelical fundamentalists as Billy Graham.

Since the late 1970s fundamentalists have embraced electoral and legislative politics and the "electronic church" in their fight against perceived threats to traditional religious values: so-called secular humanism, Communism, feminism, legalized abortion, homosexuality, and the ban on school prayer. They have continued to oppose the teaching of evolution in the schools or have sought to have creationism or intelligent design taught as well. In recent years some fundamentalists have also attacked the teaching of scientific theories on the origins of the universe (see cosmology). Those Americans who describe themselves as fundamentalists (approximately 25% of the U.S. population) have become a political bloc in their own right. During the 1980s they made up a large portion of the new Christian right that helped put Ronald Reagan into the White House, and early in the 21st cent. they aided significantly in the election of George W. Bush to the presidency. The Moral Majority, founded by the fundamentalist Baptist pastor Jerry Falwell in 1979, was the most visible example of this new trend in the 1980s; the most prominent current group is the Christian Coalition, headed by Pat Robertson. Moderate fundamentalists and conservative evangelicals continue to forge new alliances, for example in the Southern Baptist Convention, to wield political and denominational control.