Another turbulent year in the Middle East has drawn to a close, but there will be no respite in 2018 from the regional chaos that is underpinned by the inflamed rivalry of Saudi Arabia and Iran. The young crown prince Mohammed bin Salman has consolidated power, embarking on an unprecedented cultural revolution and economic reforms in Riyadh, but his foreign policy ambitions have yet to bear fruit. Instead they will continue to sap lives and resources in neighbouring Yemen, the Arab world’s poorest country, unless a political settlement is reached.