For decades Saudi Arabia and Iran have vied for influence, above all in the Islamic world, by sponsoring proxy religious and military forces in the Middle East, South Asia and Africa. At the heart of this ongoing Cold War between Riyadh and Tehran lies the Sunni-Shia divide and the intertwined histories of those who speak Arabic and those who speak Persian. Whereas Saudis frame the rivalry with their neighbours in sectarian terms, given the Wahhabi House of Saud's hostility to Shias, the leaders of Iran's clerical republic contend that monarchy, as in Saudi Arabia, is 'un-Islamic' and therefore illegitimate.