The ongoing US war with Iran, stretching month after month with no clear end, has exposed the hard limits of American power. As President Donald Trump alternates between threats and offers of peace, it’s increasingly apparent that US military force can’t easily subdue a mid-sized state like Iran — much less maintain unquestioned dominance worldwide.
Beyond the headlines of air raids, drone strikes, and naval blockades there are deeper historical forces at work. Two editorials, published some eighty years apart, illuminate the pattern: a 1942 London Times verdict that the British Empire had become “a self‑liquidating concern,” and a recent New York Times commentary arguing that the United States is now an empire in decline. Both reached similar conclusions: great powers expand under particular material and strategic conditions; when those conditions fade, empires contract.
In Britain’s case, naval supremacy, industrial primacy, and weak rivals gave way as circumstances changed. Colonies eager for self‑rule and the fiscal burden of empire forced a retreat after World War II. The same kind of transformation is underway for the United States, though in a different technological and geopolitical environment.
Why the American global order is weakening
One reason is economic redistribution. In 1945 the United States dominated the global economy; today its share of world output has shrunk as many other nations industrialized and modernized. Using purchasing‑power parity measures, China now accounts for roughly a fifth of global output while the United States sits nearer to 15 percent. That decline is not a failure so much as the predictable consequence of successful global growth the US helped architect: other countries grew faster.
Geopolitics compounds the economic story. American hegemony after World War II rested on strategic control at the ends of Eurasia: NATO in the west and bilateral pacts in the Far East. Anchored by those alliances and backed by overwhelming naval and airpower, Washington could contain rivals and shape outcomes across the Eurasian landmass, home to most of the world’s people and productivity.
That order has eroded. Decades of costly ground wars in Afghanistan and Iraq drained lives, treasure, and credibility while China invested its growing reserves in infrastructure across Eurasia through the Belt and Road Initiative. By the time the US withdrew from Afghanistan, Beijing had already deepened its influence in Central Asia. In recent years, US policy choices — including strains on NATO, provocative diplomacy over Greenland, and a new intervention in Iran — have further weakened alliances and prompted partners to seek greater autonomy.
Military overstretch has real operational costs. Munitions expended in one theater reduce the ability to deter or defend in another. The U.S. campaign against Iran, and the diversion of missile stocks and other resources, has raised doubts about Washington’s capacity to defend Taiwan and sustain commitments across the Pacific.
Energy and technological shifts
A more fundamental driver of imperial rise and fall is the energy technology of the age. Spain, the Netherlands, and Britain built empires on the technologies and energy forms of their time — slave labor, wind‑powered shipping, coal and steam. The United States’ postwar predominance was bound up with petroleum and the global energy architecture that accompanied it. As the world moves toward cheaper renewables and superior battery technologies, the material basis of American leverage is changing.
China has pushed rapidly into solar, wind, and electric vehicles, driving down costs and building dominant supply chains. Solar and wind are now often much cheaper than fossil fuels; battery advances are improving range and lowering costs for electric transport. Beijing’s scale and industrial policy have positioned it to capture large shares of EV production, solar panel manufacturing, and battery technology — sectors likely to shape economic power in the coming decades. Meanwhile, policy reversals in Washington have slowed US investment in some clean technologies.
Consequences of a shrinking American order
The retreat of a single dominant guarantor of global order will reshape international life. International institutions created under American leadership may persist, but the liberal principles that animated them — human rights, humanitarian aid, protection for refugees, and a rules‑based order — will face growing erosion. The world is likely to become more multipolar and more regionalized: ASEAN, the EU, Mercosur, and other blocs will gain importance as mediators and power centers.
A multipolar world is not inherently peaceful. Local and regional rivalries over territory, resources, water, and migration may spark intense conflicts. The Second Congo War stands as a warning of how localized clashes can produce catastrophic human losses; similar, if smaller scale, wars may recur in a world without a single stabilizing power.
Humanitarian capacity may also shrink. Cuts to foreign aid, the dismantling of development agencies, and a turn toward transactional diplomacy risk reversing progress against extreme poverty and worsening famine and disease in fragile regions. Militarization of budgets at the expense of climate cooperation will also make it harder to meet global challenges that require collective action.
Nuclear proliferation is another danger. As medium‑size states see conventional defenses fail or fear abandonment, the allure of nuclear deterrence grows. That dynamic, in a more fragmented and competitive world, raises the risk of wider proliferation and heightened crisis instability.
Why the loss of Pax Americana matters
Pax Americana had serious faults: interventions, covert operations, and hypocrisy over professed ideals were real and often tragic. Yet the American‑led order also offered predictable trade rules, development financing, and a framework that helped reduce extreme poverty dramatically over recent decades. The passing of that order may therefore be regrettable, not because the imperial era was virtuous, but because it provided some global public goods that are not easily replaced.
What comes next is uncertain. A world organized around competing regional powers, economic blocs, and new energy regimes will be more complex, with greater risks of localized bloodshed, weakened international norms, and harder collective responses to shared threats like climate change.
A personal coda
As a historian of empires, I see the arc of American power as part of a broader pattern: states rise on the back of particular technologies, institutions, and strategic postures, and they decline as those things change. While imperial America expanded opportunities and at times advanced humanitarian aims, its age is now drawing to a close. The challenge ahead is to manage that transition so the benefits accumulated under the old order — reduced poverty, international cooperation, and relative peace among great powers — do not slip away entirely.
Alfred W. McCoy is a historian at the University of Wisconsin–Madison and the author of In the Shadows of the American Century: The Rise and Decline of U.S. Global Power, among other works.
