The “primary reason why the Báb and Bahá'u'lláh chose to appear in Persia”

… the primary reason why the Báb and Bahá'u'lláh chose to appear in Persia, and to make it the first repository of their Revelation, was because, of all the peoples and nations of the civilized world, that race and nation had, as so often depicted by 'Abdu'l-Bahá, sunk to such ignominious depths, and manifested so great a perversity, as to find no parallel among its contemporaries. For no more convincing proof could be adduced demonstrating the regenerating spirit animating the Revelations proclaimed by the Báb and Bahá'u'lláh than their power to transform what can be truly regarded as one of the most backward, the most cowardly, and perverse of peoples into a race of heroes, fit to effect in turn a similar revolution in the life of mankind. To have appeared among a race or nation which by its intrinsic worth and high attainments seemed to warrant the inestimable privilege of being made the receptacle of such a Revelation would in the eyes of an unbelieving world greatly reduce the efficacy of that Message, and detract from the self-sufficiency of its omnipotent power. 

- Shoghi Effendi  (The Advent of Divine Justice)