What is the central concept of Mackinder's Heartland Theory?

The central concept of Mackinder's Heartland Theory is that control of the 'Heartland,' a vast, resource-rich area in the interior of Eurasia, is the key to controlling the world. Halford Mackinder, a British geographer, introduced this theory in his 1904 paper, 'The Geographical Pivot of History.' The Heartland, according to Mackinder, is largely invulnerable to sea power because it is a landlocked region inaccessible by naval forces. Specifically, it encompasses much of present-day Russia, Central Asia, and parts of Eastern Europe. Mackind....