The rivalry between Britain and Russia over Persia, an area now known as Iran, lasted nearly a century, and was primarily a fight to militarily control the region. Referred to by historians as "The Great Game," this battle for supremacy in expanding into Central Asia began in 1813, and ran through the early 20th century.
The Anglo-Russian Agreement of 1907 helped quell the intermittent conflict, providing a region subject to Russian influence buffered by a neutral zone. Great Britain was satisfied by the security brought by military control over India. Just a few years later, in 1910, oil was discovered in Persia, and Great Britain's focus changed. By 1915, the British military had converted its primary fuel source from coal to oil, causing a shift in political focus to protect its interests in Persian oil.