Sir halford mackinder developed what would become known as the heartland theory which suggested that interior eurasia contained a critical ""pivot area"" that would generate a state capable of challenging for world domination. the key to the area according to mackinder

The answer is Natural Protection.

Explanation:

Sir Halford Mackinder developed what would become known as the heartland theory which suggested that interior Eurasia contained a critical ""pivot area"" that would generate a state capable of challenging for world domination. The key to the area according to Mackinder wasNATURAL PROTECTION.

Mackinder is broadly recognized as the most important proponent of classical geopolitics, and his essays about the Pivot of History and Heartland are referred to in virtually all geopolitical texts. His ideas were relevant for contemporary Russia.