According to Mackinder, the Earth's land surface was divisible into:
The World-Island, comprising the interlinked continents of Europe, Asia, and Africa. This was the largest, most populous, and richest of all possible land combinations.
Later, in 1919, Mackinder summarised his theory thus: Any power which controlled the World-Island would control well over 50% of the world's resources. The Heartland's size and central position made it the key to controlling the World-Island. The vital question was how to secure control for the Heartland. This question may seem pointless, since in 1904 the Russian Empire had ruled most of the area from the Volga to Eastern Siberia for centuries. But throughout the nineteenth century:
The Russian Empire was huge but socially, politically and technologically backward—i.e., inferior in "virility, equipment and organization".
Mackinder held that effective political domination of the Heartland by a single power had been unattainable in the past because:
The Heartland was protected from sea power by ice to the north and mountains and deserts to the south.
Previous land invasions from east to west and vice versa were unsuccessful because lack of efficient transportation made it impossible to assure a continual stream of men and supplies.
He outlined the following ways in which the Heartland might become a springboard for global domination in the twentieth century :
Successful invasion of Russia by a West European nation. Mackinder believed that the introduction of the railroad had removed the Heartland's invulnerability to land invasion. As Eurasia began to be covered by an extensive network of railroads, there was an excellent chance that a powerful continental nation could extend its political control over the Eastern European gateway to the Eurasian landmass. In Mackinder's words, "Who rules East Europe commands the Heartland."
A Russo-German alliance. Before 1917 both countries were ruled by autocrats, and both could have been attracted to an alliance against the democratic powers of Western Europe. Germany would have contributed to such an alliance its formidable army and its large and growing sea power.
Conquest of Russia by a Sino-Japanese empire.
The combined empire's large East Asian coastline would also provide the potential for it to become a major sea power. Mackinder's "Who rules East Europe commands the Heartland..." does not cover this scenario, probably because the previous 2 scenarios were seen as the major risks of the nineteenth century and the early 1900s. One of Mackinder's personal objectives was to warn Britain that its traditional reliance on sea power would become a weakness as improved land transport opened up the Heartland for invasion and / or industrialisation.
Influence of the theory on other geopolitical models
Signs of Mackinder's Heartland Theory can be found in the works of geopolitician Dimitri Kitsikis, particularly in his "Intermediate Region" model. There is a significant geographical overlap between the Heartland or "Pivot Area" and the Intermediate Region, with the exception of Germany-Prussia and north-eastern China, which Kitsikis excludes from the Intermediate Region. Mackinder, on the other hand, excludes North Africa, Eastern Europe and the Middle East from the Heartland. The reason for this difference is that Mackinder's model is primarily geo-strategic, while Kitsikis' model is geo-civilizational. However, the roles of both the Intermediate Region and the Heartland are regarded by their respective authors as being pivotal in the shaping of world history.
Criticism
K. S. Gadzhev, in his book Vvedenie v geopolitiku raises a series of objections to Mackinder's Heartland to start with that the significance physiography is given there for political strategy is a form of geographical determinism.
