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.