Fundamentalism, in a religious context, is when a religious group believes that its scripture is the absolute truth, an exact representation of the world, its origins, and/or its eventual fate. Fundamentalism is a sociological movement that is observed in religions other than Christianity.
Religious influence under threat
All Christian doctrines have been in constant flux since the beginning of the religion. Throughout the medieval period, a church's doctrines were enforced by military and political power, with varying degrees of success.  Inquisitions, crusades and purges of heretics were used to suppress opponents.
The Reformation, the Enlightenment (approx. 1750 to 1800), the advance of science and increasing secularisation broke the domination of organised religion. The credibility of religious leaders was threatened by the study of the authorship of the Bible, called higher biblical criticism,  by which the Bible was read critically, just like they analyzed other ancient writings such as Homer’s Iliad and practiced by German scholars since the Enlightenment. It was realised Moses probably did not write the Pentateuch (first five books of the Bible), and that most of the prophecies were probably written after the fact.
Since their authority had been undermined, Christians who wanted to enforce their doctrine on other denominations or on secular society had to use other means of persuasion. Since the movement is largely about enforcing a belief system on outsides, it has always had a significant political aspect.
In 1874, Charles Hodge had published his three-volume Systematic Theology in which he argued that the facts in the Bible are for the faith what the facts of nature are for science.  Hodge had a powerful impact on conservative Christianity. Because of this, he might well be called the father of Christian fundamentalism.
Niagara Bible Conferences, 1883-1897
Early 20th century
A twelve volume set of essays titled The Fundamentals: A Testimony to the Truth edited by R.A. Torrey was published and distributed for free starting in 1909. It promoted the importance of basic doctrines including The Trinity, The Second Coming and inerrancy of scripture. Some of the essays argued against the higher criticism movement.
1925, Scopes Monkey Trial.
Reemergence in the late 20th century
Jerry Falwell’s Moral Majority in the 1980s is generally thought to be the formal re-immergence of Christian fundamentalism. Fundamentalism today focuses on three main items: homosexuality, abortion, and creationism. In other words, Christian fundamentalists are against equal rights for homosexuals—esp. around issues such as marriage, the adoption of children, and in some states the holding of political office. Fundamentalists are also against the teaching of evolution in public schools and against Stem cell research. In addition, they oppose a woman’s choice for an abortion under the argument that life begins at conception and therefore abortion is murder. The same Conservative fundamentalists tend to oppose state funded medical care although the death rate is higher in the United States than in other developed countries with free universal health care. They oppose killing a fetus while it is in the uterus but after a baby is born they are prepared to do less that political liberals do to keep that baby alive.
While they actually have modern origins, fundamentalists claim that they are advocating the original correct doctrines of Christianity. The idea of a "correct" interpretation is despite disagreements between Christians and even fundamentalists themselves. There is no evidence that a fundamentalist interpretation of the Bible was originally held by the early church or any time until the 19th century.
While they all agree that the Bible is the inerrant, divinely inspired, infallible Word of God, they disagree sharply on its true meaning. Broadly speaking, the movement's religious beliefs include:
- Evangelicalism (the belief in the necessity of being "born again" to gain salvation) and that their interpretation is the exclusive way to heaven. 
- Biblical literalism, regular Bible study
- Substitutionary atonement
- Spreading their religion to outsiders 
- Return of Christ in the immediate future 
- Basic personal morality on their religious affiliation.
- Belief that prayers are directly answered. 
- Faith healing 
- Direct revelation 
- Exorcism 
- Dispensationalism, the belief that God has had different arrangements with humanity throughout history.
Among US Christian evangelicals, the majority support social views such as:
- Support for torture 
- Support for war 
- Political conservatism. 
- Preference for a smaller government, which conveniently allows for a greater role for religion. 
- Opposing welfare spending by government. 
- Opposing abortion in most or all cases. 
- Opposing homosexuality and same sex marriage. 
- Personal charity or tithing. 
- Main Article: Biblical literalism
Biblical literalism entails:
- Young-Earth creationism and opposition to mainstream evolution.  However, there is limited acceptance of divinely guided evolution. 
Christian fundamentalists are more effective at driving sin underground than preventing it. This leads to hypocritical stances on many social issues.
- "States that banned gay marriage had 11 percent more porn subscribers. The level of agreement in a state with the statement that "Even today miracles are performed by the power of God" predicted higher pornography consumption. States claiming to have old-fashioned values about family and marriage purchased substantially more adult-content subscriptions."
Why is this? The more sexual repression there is in a state or a community the more people are tempted or driven to find whatever outlet they can.
Many Muslim fundamentalists adhere to a traditionalist Salafi/Wahhabist interpretation of Islam. Some terrorist organizations follow or promote an extreme version of Salafi Islam. Within the Salafi movement, emphasis is placed on teaching: 
- strict monotheism (tawhid)
- avoidance of innovation in religious matters (bida’a) and
- loyalty to Islam and disloyalty to anything un-Islamic (wala wal baraa)
- personal interpretion ijtihad in interpreting Islamic law, outside of the traditional taqlid interpretation schools.
- Quranic literalism
- religious sharia law as core part of religion
- "It is far easier to obey without thinking. [...] in the last 100 years, Islam has been sliding back to an era that never really existed. "
Ironically, the movement's origins only go back to the 18th century, based on the revivalist teachings of Muhammad ibn Abd al-Wahhab (1703–1792).
Peer group pressure
- "It is outside politics or religion. It is about certain individuals who come together for the thrill of being part of something bigger. It is a youth subculture ... and peer groups play a big role "
Responses to fundamentalism
While fundamentalists have often been violently suppressed or attacked, it is questionable if this is an effective approach since it may drive more people to join their cause. Others have called for a dialogue with fundamentalists in the hope of moderating their views.
"Let us therefore reject all superstition in order to become more human; but in speaking against fanaticism, let us not imitate the fanatics: they are sick men in delirium who want to chastise their doctors. Let us assuage their ills, and never embitter them, and let us pour drop by drop into their souls the divine balm of toleration, which they would reject with horror if it were offered to them all at once."
- — Voltaire
- ↑ 381 A.D. Heretics, Pagans, and The Dawn of the Monotheistic State
- ↑ 
- ↑ 
- ↑ Marsden, George M. "Fundamentalism and American Culture." New York, Oxford University Press, 1980.
- ↑ Noll, Mark A. "A History of Christianity in the United States and Canada." Grand Rapids, MI, William B. Eerdmans Publishing Co., 1992.
- ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 
- ↑ 
- ↑ Protestants and Frequent Churchgoers Most Supportive of Iraq War, Gallup, March 16, 2006
- ↑ 9.0 9.1 9.2 9.3 9.4 9.5 
- ↑ 
- ↑ Hassan Hassan, The secret world of Isis training camps – ruled by sacred texts and the sword, The Observer, 25 January 2015
- ↑ Comment by Juvegirl
- ↑ The story of a radicalisation: 'I was not thinking my thoughts. I was not myself'
- Barr, James. "Fundamentalism." London, SCM Press, 1977.
- Harding, Susan Friend. "The Book of Jerry Falwell: Fundamentalist Language and Politics." Princeton, NJ, Princeton University Press, 2000.