The Allied faction, most notably the British, has gained the upper hand during the first world war due to their acquisition of various oil fields. The oil has powered their military vehicles most notably its naval fleet and the introduction of Mark V tanks that posed significant advantage at the course of the war.
The British secured access to oil during World War I and beyond by buying a majority stake in the Turkish Petroleum Company.
During World War I, oil was an asset of vital importance to all nations. British already had control over large oil reserves in Persia, where Iran is now, and they sought to have control over as many oil reserves as possible.
