Over time, a number of movements have emerged in Protestantism that cut across these traditions. By the twentieth century, many historic Protestant denominations had become more theologically liberal, though they still contained conservative congregations and individuals. In the 1920s, they came to be known as “mainline” Protestant churches, and they include representatives of all the major Protestant traditions except Pentecostalism.
Mainline denominations were criticized by more conservative ones, who came to be called “fundamentalists” because they favored The Fundamentals—a twelve-volume set of books advocating conservative positions. Over time, the origin of the term was largely forgotten, and today fundamentalist is a term used to refer to very conservative Protestants (as well as members of other groups and even other religions, e.g., “fundamentalist Muslims”). The term also has taken on negative connotations. If someone is called a fundamentalist, it suggests that he is doctrinally rigid and hostile to other viewpoints. For this reason, the term should be used only for those few Christians who apply it to themselves. Otherwise, it becomes an insult that adds more heat than light.
Because of the negative connotations the term acquired, conservative Protestants needed a different and more positive term for themselves, and in the United States they began to call themselves “evangelicals.” This can be confusing since the term evangelical has been used in other senses. In Europe, it is applied to mainline Protestant churches or, alternately, to anyone who strongly favors evangelism (i.e., preaching the gospel).
However, in the United States evangelical generally indicates a conservative Protestant who distances himself from the rigidity associated with fundamentalism, though the term is fluid and not all who identify themselves as evangelical fit this profile.