Sir Halford Mackinder's Heartland Theory, proposed in 1904, is a foundational concept in geopolitics. It posits that the 'Heartland' – a vast landmass in Eurasia, largely inaccessible to sea power (encompassing parts of Eastern Europe and Central Asia) – is the strategic pivot of the world. Mackinder famously stated: 'Who rules East Europe commands the Heartland; Who rules the Heartland commands the World-Island (Eurasia and Africa); Who rules the World-Island commands the World.' The theory divided the world into the Heartland, the 'Inner Crescent' (rimland of Eurasia), and the 'Outer Crescent' (Americas, Australia, insular powers).

In Mackinder's view, the Heartland's immense resources, strategic depth, and large population made it a formidable base for global power, especially if controlled by a single dominant land power. The theory influenced geopolitical thinking during the Cold War, with the US 'containment' strategy aimed at preventing Soviet expansion into the Inner Crescent and beyond.

In the contemporary geopolitical scenario, the direct military implications of the Heartland theory have evolved but its core ideas retain relevance. While air power, nuclear weapons, and sea power have diminished the absolute invulnerability of the Heartland, the strategic importance of Eurasia remains paramount. Russia, controlling a significant portion of the historical Heartland, continues to exert influence over Eastern Europe and Central Asia, as seen in conflicts like Ukraine. China's Belt and Road Initiative (BRI) can be interpreted as a modern attempt to integrate the World-Island economically, creating new land-based trade routes and spheres of influence across the Eurasian landmass, effectively challenging traditional maritime dominance. The competition for resources (especially energy), control over critical infrastructure, and the demographic potential of the region still make the Heartland a crucial arena for global power projection and competition between major powers like the US, China, and Russia. Thus, while the means of control have diversified, the geographical significance of Eurasia as a strategic pivot endures.