Why US-led security alliances in Asia are losing coherence

Geopolitics, at its core, examines how geography shapes international politics, power distribution and security dynamics. One enduring idea is geographer Halford Mackinder's "heartland" theory, which situates Eurasia as the central arena of global power competition. In 1904, Mackinder argued that the vast land mass of Europe and Asia – what he called the "world island" – contained a pivotal core, the "heartland", rich in resources, population and strategic depth. His dictum – "Who rules Eastern Europe commands the Heartland/Who rules the Heartland commands the World Island/Who rules the World Island commands the world" – captures the essence of this geographical determinism.

Mackinder's theory finds striking resonance. Major global conflicts from the two world wars to the Cold War have indeed centred around or been deeply influenced by struggles over Eurasian dominance. More recent conflicts, such as the Iraq war and current wars in Ukraine and Iran, also reinforce the idea that Mackinder's heartland remains geopolitically decisive.

The resurgence of conflict in the heartland has reshaped the global security environment. Over the past decade, US strategic thinking has increasingly shifted towards the Indo-Pacific, beginning with the Obama administration's pivot to Asia. The US aimed to counterbalance China's rise by reviving the Quadrilateral Security Dialogue with Japan, India and Australia, and establishing the Aukus security pact with Britain and Australia. These alliances were designed to consolidate maritime power and contain China's influence in the Indo-Pacific.

But this strategic focus has been disrupted by the intensification of geopolitical density in Eurasia and US President Donald Trump's global tariff war. The new developments demand attention, resources and political capital, weakening the coherence and effectiveness of US-led alliances in Asia. India, for instance, has been affected by higher US tariffs, prompting elites to question the value of a closer security alignment with the United States. The global security architecture is no longer centred on a single theatre; instead, it is stretched across multiple fronts, creating uncertainty and weakening alliance cohesion.