- invent an existential threat
- convince gullible people that it threatens them personally
- get money and power from them to "fight" it
- use some of that money and power to make your message more convincing and to broadcast it more widely
This may involve the creation or consolidation of a new belief-tribe (e.g. fear of divine retribution was used to convince evangelicals in the 1980s to form the core of the anti-abortion movement, politically fracturing the Christian base which had previously tended to side with liberal causes) or it may exploit one that already existed (said evangelicals later being ripe picking for anti-gay hatred, among many other things).
The threat is usually but not always some other group (i.e. demonization), since it is easier to convince gullible people that other people are a danger than to convince them that natural phenomena (e.g. global warming) pose a danger.
Religious fundamentalists are particularly prone to believing threats of divine retribution in the afterlife, even if there is no scriptural support for the claim in question, and are therefore often used as patsies for fearmongery.
The Bush-Cheney administration exploited the emotional trauma resulting from the 9/11 attacks to promote a general culture of fear in the United States during the first decade of the 2000s, which enabled the right wing establishment to push through many agenda items that the public had resisted for many years, including sharp reductions in overall liberty and in accountability for the powerful. This trend shows no signs of abating as of this writing (2015), though it does seem to be gradually changing in nature.