Les empires, ainsi que les hommes: Montesquieu and the American Age

By Matthew Parish

Tuesday 22 September 2026

There is a melancholy sentence associated with Montesquieu’s study of Rome: Les empires, ainsi que les hommes, doivent croître, dépérir et s’éteindre — empires, like men, must grow, decline and die. Strictly speaking, the words are d’Alembert’s, written in his Éloge de Montesquieu while describing Montesquieu’s analysis of Roman greatness and decline. Yet they express so perfectly the historical philosophy of Montesquieu’s Roman writings that they have acquired a life of their own. Political orders are not permanent. The institutions that produce their greatness may eventually produce their weaknesses, and the causes of decline may be visible only in retrospect.

The temptation to apply this proposition to the contemporary United States is obvious. America emerged from the Second World War with an extraordinary concentration of economic, military, technological and cultural power. The Soviet Union subsequently disappeared. European empires dissolved. For a period after 1991, the United States occupied a position in the international system for which there was scarcely a modern precedent. American military power reached across the planet, the dollar served as the principal currency of international exchange, American universities attracted intellectual elites from everywhere and American technology companies constructed much of the infrastructure upon which the emerging digital world depended.

Nevertheless the language of decline must be used carefully, because relative decline is not the same thing as decadence, collapse or extinction. The United States remains an immense economic power. World Bank figures put American nominal GDP in 2025 at about $30.8 trillion, compared with approximately $19.5 trillion for China. The American economy represented roughly a quarter of world output measured at current exchange rates. Its GDP per head remained vastly higher than China’s, and the country continued to attract substantial net migration. These are peculiar characteristics for an empire supposedly approaching extinction.

Yet Montesquieu’s insight was subtler than the proposition that rich countries suddenly become poor. Rome did not cease to be powerful because somebody else acquired a larger economy. Political systems decline when the relationship between their institutions, ambitions and resources becomes progressively harder to sustain. That is the more interesting analogy with contemporary America.

The republic that became an empire

The United States has always possessed an uneasy relationship with the idea of empire. She was born in revolt against one. Her constitutional culture remains republican and her political vocabulary is saturated with hostility towards imperial government. Americans elect presidents rather than emperors, Congress retains enormous constitutional authority and the states preserve extensive powers of their own. The American constitutional structure was itself influenced by Montesquieu: the separation of legislative, executive and judicial authority reflected precisely the fear that concentrated political power would extinguish liberty.

Nevertheless an empire need not possess colonies governed by proconsuls. Empire may also describe a system in which one state provides the principal military architecture, financial currency, technological infrastructure and diplomatic framework within which numerous other states operate. Under that broader definition, the post-1945 United States acquired unmistakably imperial characteristics, albeit characteristics radically different from those of Rome, Britain or France.

Washington accumulated obligations across continents. American security became connected with European security, Middle Eastern security and East Asian security. The dollar became entangled with the reserves, debts and commercial transactions of countries that might simultaneously resent American political influence. American financial sanctions acquired international force because so much of global finance passed through institutions exposed to American jurisdiction. The extraordinary attraction of American universities, entertainment and technology complemented this hard power with something more difficult to quantify: the ability to define much of the intellectual and cultural language of modernity.

This system was enormously advantageous to the United States, but it also generated obligations. Empires are expensive not merely because armies cost money. They are expensive because the hegemonic state gradually becomes responsible for preserving a system whose beneficiaries may have considerably less incentive to pay for it.

The fiscal problem

Here the contemporary American position becomes more recognisably Montesquieuan. The Congressional Budget Office projected in February 2026 that federal debt held by the public would stand at about 101 per cent of GDP in 2026 and rise to 120 per cent by 2036 under its then-current-law baseline. It projected a 2026 federal deficit of $1.9 trillion, or 5.8 per cent of GDP, while net interest expenditure was projected to exceed $1 trillion. These are projections rather than destiny, and future Congresses can change taxation and expenditure. Nevertheless they identify a structural problem: the American state has accumulated commitments more rapidly than it has established the fiscal means of paying for them.

This does not mean that the United States is about to become insolvent. Comparisons between sovereign states and households are generally misleading, and the United States possesses unusual financial advantages because it issues the world’s principal reserve currency and supports extraordinarily deep capital markets. The more interesting problem is political. Interest payments consume resources that cannot simultaneously be spent on defence, infrastructure, scientific research or social programmes. CBO’s February 2026 baseline projected net interest expenditure rising from 3.3 per cent of GDP in 2026 to 4.6 per cent in 2036.

Montesquieu might have recognised the mechanism. Great powers frequently become prisoners of the institutions created during their ascent. Programmes established in one generation become obligations in another. Military commitments undertaken under one strategic environment survive into the next. Tax privileges accumulate constituencies. Every individual commitment may be politically defensible, while their aggregate becomes increasingly difficult to finance.

Decline therefore need not arrive through catastrophe. It may emerge through arithmetic.

The multiplication of rivals

The second transformation is geopolitical. The post-Cold War moment in which no other state could plausibly challenge American predominance was historically unusual and could hardly have lasted indefinitely. China has acquired enormous industrial and technological capacity. Russia, despite possessing a much smaller economy, has demonstrated that military power and willingness to absorb losses can disrupt the security architecture of an entire continent. India is growing in economic and diplomatic significance. Middle powers increasingly pursue policies that do not fit comfortably into a binary division between an American system and its adversaries.

None of this necessarily entails American disappearance. It means instead that Washington increasingly operates in a world in which the price of imposing its preferences is higher.

This distinction matters. Britain did not cease to exist when the British Empire declined. France did not cease to matter when she lost Algeria and Indochina. The Netherlands survived the disappearance of a commercial empire that had once reached across oceans. The end of imperial predominance and the destruction of the underlying state are entirely different historical phenomena.

The United States may therefore experience what might be called imperial contraction without national decline in any straightforward sense. Indeed contraction could conceivably strengthen her if commitments were brought into closer alignment with resources. An empire can become weaker while the country at its centre becomes more sustainable.

The internal republic

There is another Montesquieuan question, perhaps more important than military expenditure or relative GDP: what happens to the domestic political institutions of a republic that exercises enormous power abroad?

Montesquieu was preoccupied with institutional balance because liberty depended upon power checking power. The American constitutional system deliberately incorporated this insight. Congress, the Presidency and the judiciary were given different sources of authority precisely because no single political institution was supposed to embody the state.

The difficulty for modern America is that an eighteenth-century constitutional structure must govern a twenty-first-century administrative, military, financial and technological superpower. Decisions may have consequences almost instantly across the world. Nuclear weapons cannot sensibly be commanded by congressional committee. Cyber operations, financial sanctions, intelligence activities and emergency economic measures demand degrees of executive speed unimaginable to the authors of the Constitution.

The resulting tension is structural rather than uniquely attributable to any one President or party. Modern government rewards concentrated executive action while the American constitutional tradition distrusts concentrated executive authority. The stronger America became internationally, the more difficult it became to reconcile the practical requirements of global power with the deliberately cumbersome constitutional machinery of a republic.

That may prove one of Montesquieu’s most important insights for the American future. Institutions created to restrain power can become frustrated by the demands of exercising enormous power. Yet abandoning those restraints in the interests of efficiency risks damaging the political order whose preservation was the purpose of power in the first place.

Polarisation and the loss of a common story

Empires also depend upon narratives. Rome had Rome. Britain possessed an elaborate conception, however self-serving and frequently contradicted by reality, of civilisation, commerce and constitutional government. The Soviet Union possessed Marxism-Leninism. The American international system developed its own narrative around constitutional democracy, markets, individual liberty and a rules-based international order.

The difficulty arises when the population at the centre of an imperial system ceases to agree about what the system is for.

Contemporary American political disputes increasingly concern not merely different policies but different accounts of the country itself. One account emphasises a constitutional republic whose global responsibilities derive from the defence of a liberal international order. Another emphasises national sovereignty and argues that international commitments have extracted disproportionate costs from American citizens. Other perspectives emphasise inequalities within American society or contradictions between proclaimed universal values and historical practice.

These disagreements are not themselves proof of decline. Fierce political conflict is hardly new in American history; the republic survived a civil war, political assassinations, economic depressions, racial violence and periods of profound institutional dysfunction. Historical memory should therefore make us suspicious of claims that contemporary disagreement is unprecedented.

Yet an imperial system ultimately requires some domestic agreement about the reason for maintaining it. If citizens conclude that foreign commitments do not serve them, those commitments eventually become politically fragile. No empire can indefinitely maintain a conception of international responsibility that its own population has ceased to regard as legitimate.

Technology and the possibility of renewal

Here the analogy with Rome begins to break down. Historical analogies often become misleading precisely when they become most seductive.

The United States possesses capacities for renewal that ancient empires did not. She remains a magnet for migrants, entrepreneurs, scientists and capital. Her enormous internal market allows successful innovations to scale rapidly. American universities remain central institutions in global research, while American firms have played leading roles in artificial intelligence, software, biotechnology, aerospace and advanced computing. The very technological revolution that may destabilise existing political and economic structures may also provide America with another period of exceptional economic power.

This is why deterministic theories of American decline are unsatisfactory. Empires are not biological organisms. They do not possess chromosomes instructing them to die at a particular age. Rome is useful because she demonstrates that political institutions can generate both strength and weakness, not because every great power must reproduce Roman chronology.

Indeed one might reverse the analogy. Artificial intelligence may enable a state to administer complexity on a scale previously impossible. Technologies of automation could increase productivity, accelerate scientific discovery and reduce the administrative burden of government. If the United States remains disproportionately successful in developing and deploying those technologies, then the twenty-first century could produce not the exhaustion of American power but its transformation.

The danger is that technological strength and political strength are not identical. A society can possess brilliant companies while maintaining dysfunctional public institutions. It can generate extraordinary private wealth while accumulating unsustainable public liabilities. It can dominate artificial intelligence while failing to maintain bridges, electricity grids or political confidence. Montesquieu would presumably have been interested less in the existence of ingenious machines than in whether institutions could incorporate their consequences without destroying the balance upon which liberty depended.

What does it mean for an empire to die?

The greatest weakness in applying the famous dictum to the United States lies in the word s’éteindre. Empires seldom extinguish themselves as neatly as human beings die.

Rome itself demonstrates the problem. The Western Roman Empire conventionally ended in AD 476, yet the Eastern Roman Empire survived for almost another millennium. Roman law outlived both. Roman political vocabulary survives in republics and senates across the world. Christianity, transformed by Roman institutions, became one of the foundations of European civilisation. An empire can therefore disappear territorially while continuing to govern the imagination of its successors.

The same was true of Britain. The British Empire largely disappeared, but English became the principal international language. Common-law systems survived across former colonies. London remained an important financial centre and parliamentary institutions developed in countries that had rejected British rule. Imperial extinction turned out to be accompanied by remarkable institutional survival.

American power may eventually undergo something similar. The United States need not permanently maintain hundreds of overseas facilities or occupy the predominant position in every region for American civilisation to remain enormously influential. The internet, modern finance, popular culture, university education, corporate organisation and the language of constitutional rights have already absorbed American assumptions to an extraordinary degree.

An American imperial order might therefore diminish while an Americanised world persisted.

The hidden causes of decline

The most interesting part of d’Alembert’s formulation is actually what follows the famous sentence. The revolutions through which empires rise and fall, he suggested, frequently have hidden causes obscured from contemporaries by their apparent insignificance.

That observation deserves more attention than the dramatic imagery of death.

If American predominance is eventually regarded by historians as having declined during the early twenty-first century, the decisive causes may not be the events contemporaries currently imagine. They may not be a particular election, war or diplomatic crisis. They may instead be apparently mundane processes: accumulated public debt, demographic changes, deteriorating infrastructure, transformations in educational quality, the concentration or diffusion of technological expertise, changing patterns of migration, the gradual alteration of the international monetary system or a loss of public confidence in institutions.

Conversely, some of the phenomena currently presented as symptoms of decline may eventually look trivial. Political turbulence is highly visible, whereas institutional adaptation is slow and boring. History consequently tempts contemporaries to exaggerate spectacle and underestimate structure.

This is precisely where Montesquieu remains useful. His great subject was not simply why Rome fell. It was why Rome became great, and how some of the processes associated with greatness eventually altered the institutions that had created it.

America after the American empire

The most productive application of the dictum to contemporary America is therefore not the prediction that the United States is dying. There is little empirical basis for such melodrama. A country with an economy exceeding $30 trillion, immense technological capabilities, extraordinary capital markets, a population of more than 340 million and continuing attraction to migrants is not readily described as approaching extinction.

The more serious question is whether the particular form of American predominance created between 1945 and 1991 can continue indefinitely. History provides little reason to suppose that any international distribution of power is permanent. Other countries develop. Technologies diffuse. Alliances change. Domestic priorities alter. Institutions designed for one historical environment struggle with another.

Hence the Montesquieuan proposition is difficult to escape. The American empire, if that is what we choose to call the international order centred upon American military, financial and technological predominance, will not last forever. Nothing political does.

But that tells us surprisingly little about the future of the United States. The country might respond to relative geopolitical contraction by becoming richer, more technologically advanced and more internally coherent. Alternatively, she might attempt to preserve every inherited international commitment while simultaneously refusing the taxation and institutional reform required to finance them. The former would represent adaptation. The latter would reproduce one of history’s familiar imperial dilemmas: an expanding discrepancy between obligations and resources.

Montesquieu’s enduring lesson is therefore not fatalism. It is almost the opposite. Political orders contain causes. Institutions have consequences. Greatness and decline are not mysterious acts of providence but historical processes that can, at least imperfectly, be understood.

The United States is unusual because the philosopher whose ideas illuminate the problem also helped inspire the constitutional architecture through which America might address it. Montesquieu contributed intellectually to the system of divided powers that became characteristic of the American republic. That system is frustrating, slow and frequently disorderly because it was designed to prevent the easy concentration of political authority.

It may turn out to be America’s weakness. It may also turn out to be the reason for her survival.

Empires grow, decay and disappear. Republics, however, can reinvent themselves. The crucial question for the United States in the twenty-first century is therefore not whether she can escape history. She cannot. It is whether, as one historical form of American power changes, the constitutional republic beneath it proves capable of changing too.