In just 24 hours, Saudi Arabia’s crown prince launched an oil-price war with Russia and sidelined a domestic rival to cement his power at home. But his surprise actions on the world stage and within his own kingdom were set in motion months ago. As Saudi Arabia was gearing up to sell shares in Saudi Aramco, its national oil company, late last year, Crown Prince Mohammed bin Salman had teamed with Russia to limit oil production and keep prices high. But that partnership was faltering. And in the weeks leading up to the December…