Promulgating belief and promoting ideas that someone or something unknown is controlling individual lives, countries or the world.
A good conspiracy theory requires the following qualities: (a) it must be difficult, better still, impossible, to understand at first glance; (b) it must contain a large number of leads and loose ends, with always one more left to chase; (c) the story should speak to a wider truth about society, through a series of disconnected or unconnected or unfalsifiable propositions; (d) there should be no easy way of verifying it.
Conspiracy theory was pioneered and popularized in the UK by Nesta Webster. She had a distrust of cults and secret societies whose true purpose, as she saw it, was to undermine religion and bring about the downfall of civilization. She promoted the idea of an international Jewish-Bolshevik conspiracy and also identified occult powers at work behind international finance, theosophy and grand orient masonry.
Rich material for modern conspiracies is provided by (a) alien encounters, (b) secret, power elites from business, politics and diplomacy; (c) freemasonry and other secret societies; and (d) the assassination of President Kennedy.