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.

Through adroit diplomacy, mobilising forces such as Hezbollah and deploying its Revolutionary Guards in the Syrian War, but above all because of President Bush's disastrous invasion of Iraq, Iran has expanded its influence in Iraq, Syria and Lebanon. Saudi Arabia’s hyperactive Crown Prince, Muhammad bin Salman, has responded by intervening in Yemen, isolating Qatar and destabilizing Lebanon. None of MBS’s foreign adventures has fared well, in contrast to his domestic reforms: re-opening cinemas and ending the ban on women driving. Barring his overthrow, Salman will remain in power for decades, hence the Islamic cold war is unlikely to end any time soon.