The term fundamentalism was first used in the United States to refer to a movement in Protestantism that demanded strict adherence to biblical doctrines (as interpreted by sect leaders). Fundamentalism may be found in almost any religion, notably what is referred to by non-Muslims as Islamic extremism.
The societal import of fundamentalism is that believers seek to extend the religious sphere to encompass all aspects of life, including education and government. This is apparent in the US with Christians who want to replace separation of church and state with “one nation under God,” which is already woven into the pledge of allegiance by a 1954 act of Congress.
In affluent nations, such as the United States, the appeal of fundamentalism is often based upon rejection of moral relativism, racial integration, and cultural pluralism. There is also the desire to unearth moral absolutes in the morally corrupt society.
In the Islamic world, fundamentalism reflects the failure of the ruling elites to deliver on their promises of well-being for the masses in their societies.
The stridency of fundamentalism easily slips into militancy. In the instance of Islamic fundamentalists, non-believers are considered enemies, not worthy of breath, whence the relentless worldwide campaign of terror.
Generally speaking, the errors in religion are dangerous; those in philosophy only ridiculous. ~ David Hume