The grinding U.S. confrontation with Iran has exposed a simple but uncomfortable fact: American military dominance can no longer unilaterally impose order across the globe. As administrations swing between threats and offers of détente, the episode around the Persian Gulf reveals deeper, longer-term shifts that are steadily eroding Washington’s global primacy.
Two editorials, separated by roughly eighty years, illuminate this transformation. In 1942 the London Times, despite Britain’s wartime struggles, concluded that the imperial system that had rested on naval supremacy, industrial power, and the weakness of rivals was already “self-liquidating.” By the mid-1940s those temporary advantages began to dissolve and colonies sought self-rule. A recent New York Times commentary made a similar case for the U.S.: after eight decades of leading a world order, America may now be an empire in retreat.
That comparison helps explain why the Iran crisis matters beyond headlines. The U.S. once presided over a liberal international system built around institutions, trade rules, and a military architecture that anchored its influence across Eurasia. Erosion on economic, geopolitical, and technological fronts has steadily narrowed Washington’s room to maneuver.
Economically, the story is straightforward: for much of the postwar era the United States dominated global output; over time that share declined as other countries industrialized and grew. Far from being proof of failure, that diffusion of wealth is partly a signal of U.S.-led globalization’s success — but it also means Washington must now bargain with many peers and rivals rather than dictating terms. China’s rise as an economic powerhouse, India’s growth, and the maturation of regional blocs have all reduced U.S. unilateral leverage.
Geopolitically, the U.S. built its power by anchoring both ends of Eurasia. NATO in the west and bilateral alliances in East Asia formed a containment perimeter across the continent, backed by a global network of bases and maritime strength. But missteps and overreach weakened that position. Long, costly occupations in Afghanistan and Iraq diverted resources and attention at a moment when China was accumulating capital and extending influence across Eurasia with infrastructure and trade initiatives. The U.S. military withdrawal from Afghanistan in 2021 marked a tipping point in the balance of influence in Central and South Asia.
Political decisions of the last few years have also strained alliances. Moves that undermined NATO cohesion and actions that disrupted supplies critical to Asian partners—tied to conflicts in the Middle East—have created doubts about U.S. reliability. Depleting missile inventories and signaling lower priority for Asia raise questions about America’s ability to defend Taiwan and maintain the Pacific security perimeter. Any loss of Taiwan would push U.S. reach back toward the second island chain and inflict a decisive strategic setback.
Energy and technology are equally decisive. Historically, empires have ridden the dominant energy and production systems of their era: plantation slavery, wind and sail, coal-powered industry, and — in the 20th century — oil. American hegemony was tightly intertwined with petroleum. Today the global energy transition and advances in batteries and solar manufacturing are reshaping comparative advantage. China has invested heavily in renewable capacity, scaled solar-panel production, and moved rapidly into electric vehicles and battery technology. Falling costs for wind and solar, alongside battery improvements, threaten to make fossil-fuel–dependent industries and regions less competitive.
U.S. policy has been inconsistent. Federal investments under the previous administration aimed to accelerate the green transition, but recent policy reversals have boosted fossil fuel extraction and rolled back incentives for renewables and electric vehicles. Those shifts risk ceding industrial leadership in key sectors to nations that have prioritized both scale and supply-chain control.
The consequences of this systemic shift are profound. The Pax Americana that helped stabilize global trade, reduce extreme poverty, and undergird postwar institutions is giving way to a multipolar world in which regional powers and blocs will exercise greater influence. That can mean more complex diplomacy, but also more localized competition and conflict. Regional rivalries over territory, water, minerals, and migration could flare into sustained violence, as the wars in central Africa showed in the late 1990s and early 2000s.
At the institutional level, the formal frameworks the U.S. helped create—the UN system, the Bretton Woods institutions, the WTO—may endure, but the liberal principles that animated them—human rights, humanitarian commitments, refugee protection—are under strain. Shifts toward transactional diplomacy and pragmatic, interest-driven statecraft, exemplified by major economic actors, risk hollowing out the ethical commitments that sustained international cooperation.
Humanitarian consequences are immediate. Cuts to development and aid programs reduce capacity to prevent famine, disease, and displacement; even modest reductions in assistance can translate into millions of additional deaths and suffering. At the same time, military budgets are rising worldwide, including significant investments in nuclear arsenals. If medium-sized states perceive conventional defense as unreliable, more of them may seek nuclear deterrence, increasing proliferation risks.
There is also a climate dimension: the resources nations divert to rivalry and rearmament will compete with those needed for collective responses to climate change. Failure to coordinate on decarbonization and adaptation will magnify human and economic costs, particularly in vulnerable regions.
For many, the decline of unipolar American leadership will be welcomed; the world will no longer be ordered by a single hegemon. Yet the historical record suggests mixed outcomes. American global power, for all its faults and contradictions, provided a framework that reduced certain kinds of interstate violence and supported large-scale economic development. Its retreat may open space for alternatives that are less committed to liberal norms and humanitarian priorities.
That loss matters. Within the narrow bounds of empire, Pax Americana facilitated institutions and flows that improved living standards for hundreds of millions. The passing of that era will not automatically produce a safer or fairer world.
Alfred W. McCoy is a historian of empires and author of books on U.S. global power and intelligence practices. His work examines how technological change, energy systems, and strategic choices shape the fortunes of great powers. This essay reflects those themes and argues that the American century, like the earlier British one, has entered a phase of irreversible retrenchment with wide-reaching consequences for global order.
