The Rule of Empires: Those Who Built Them, Those Who Endured Them, and Why They Always Fall, by Timothy H. Parsons, Oxford University Press, $29.95

Merchant Kings: When Companies Ruled the World, 1600–1900, by Stephen R. Bown, Thomas Dunne Books, $26.99

After the terrorist attacks of September 11, 2001, it became fashionable on the right, and among some hawkish liberals, to defend and even promote the idea of an American Empire to keep us safe from terrorists, hold rogue nations in check, and secure global commerce. It's true that Pax Americana's chief boosters believed in empire long before "everything changed"; the neoconservative historian Robert Kagan wrote a 1998 article in Foreign Policy, for example, celebrating the United States as a "benevolent empire." But the attacks on the Pentagon and World Trade Center provided new momentum for the imperial cause. A month after the attacks, Max Boot published "The Case for American Empire" in The Weekly Standard, arguing that 9/11 "was a result of insufficient American involvement and ambition; the solution is to be more expansive in our goals and more assertive in their implementation."

In the middle years of the last decade, as the wars in Iraq and Afghanistan grew steadily worse, this jingoism fell out of favor, leaving only a shrinking core of committed neoconservatives to champion the virtues of empire. Still, the questions posed by American global military dominance were far from settled in public opinion. In March, when President Barack Obama ordered the bombing of Libya and the enforcement of a no-fly zone, introducing American military hardware into a contentious Arab Spring for the first time, disputes over Washington's proper global role were again thrust to the fore of public debate.

Relatively few Americans question the morality or utility of their country's power, even if there is substantial disagreement about how and when that power should be used. Advocates of empire sometimes acknowledge that ruling the world through military might requires a great deal of violence, but they argue that this is the price of security and prosperity. Two recent histories of previous great empires argue instead that the imperial project is inherently unstable.

The Rule of Empires, by the Washington University historian Timothy Parsons, explores the fundamental contradictions of imperial rule, making the case that empires have become increasingly difficult to maintain as potential subjects' identities have become less fluid and more nationalistic. In Merchant Kings: When Companies Ruled the World, 1600–1900, the independent historian Stephen Bown takes a less systematic approach to the study of imperial power, but his book supplements Parsons' by filling in the biographical details of the men who built Europe's modern commercial empires. Both books demonstrate that while empire may seem a quick route to power and wealth, in the long run the idea is a military and financial loser.

Parsons studies seven empires, searching for the features they have in common. His selections seem designed to illustrate the point that the conquerors become the conquered and vice versa. Britain was once a remote outpost of the Roman Empire, but many centuries later Britain's might would far eclipse that of its former masters, covering a quarter of the world's people and lands as far-flung as India and Kenya. The Umayyad Muslims controlled parts of Spain for more than 700 years, but once Spain was united as a Christian kingdom its rulers wasted little time in seizing a South American empire from the Incas. Napoleon led the French to dominate continental Europe, including the former Roman heartland of Italy, which the French treated as a backwater inhabited by savages. They were repaid in kind when the Nazi empire stormed across France in 1940, shocking and embarrassing an ostensibly formidable imperial power.

Parsons argues that empires, contrary to popular opinion, are extremely vulnerable to conquest. Invaders can turn established rulers' subjects against them and, once in power, expropriate the centralized administrative systems already in use. When a small number of Spanish conquistadors under Francisco Pizarro attacked the Incan Empire ruled by Atawallpa, they took advantage of the civil strife that had begun after the death of Atawallpa's father. Pizarro and his men were assisted by numerous Incans who sought a better life after Atawallpa's tyrannical rule, including several of his brothers, who hoped to claim the throne. "In effect," Parsons writes, "the conquistadors enlisted New World peoples in their own subjugation." Firmly ensconced in power, the Spanish used Incan roads and detailed censuses to exploit populations long accustomed to imperial rule.

Parsons contrasts this gaping hole in the seemingly impenetrable armor of empire with the resilience of stateless societies. For example, the Nandi, an East African people who live in what is now Kenya, spent a decade successfully fighting off far more heavily armed British imperialists at a time when England was at the height of its power. Parsons does not mention them, but the Mapuche Indians illustrate the point even more dramatically: They resisted both the Incan Empire and the conquistadors, maintaining a large degree of independence well into the 19th century without any centralized political authority.

Empires throughout history have claimed "to rule for the good of their subjects," Parsons maintains, but this "was and always will be a cynical and hypocritical canard. Empire has never been more than naked self-interest masquerading as virtue." To keep resources flowing from subjects to rulers, empires must walk a tightrope between subjugation and assimilation. If the state imposes draconian laws and taxes, it will face rebellion, so the rulers must seek out collaborators among their subjects who will assist in the domination of their fellow citizens. In return, collaborators are frequently brought into the imperial fold and given a portion of the spoils. But this leaves the empire vulnerable to conquering from the inside out, with many masters and few servants.

Muslim Spain during the Middle Ages—or al-Andalus, as it was called—faced the latter problem more severely than any other empire Parsons examines, because it was animated by the universalistic creed of Islam. Spanish Christians and Jews were "peoples of the book" (dhimmi) and entitled to practice their religions, provided they paid a head tax known as the jizya. Pagans could be exploited further, possibly through outright enslavement. But any Muslim was theoretically free of these restrictions, and conversion was as simple as publicly declaring, "There is no God but God and Muhammad is his prophet." Parsons explains the conundrum this situation created for the Andalusians: "Proselytizing religion provided a moral excuse for empire building, but it also blunted the extractive power of imperial rule. More seriously, the subject majority threatened to hijack the imperial enterprise as they became Muslims in ever larger numbers."

Not surprisingly, Islamic imperialists resolved the conflict between spiritual duty and worldly goods by altering their faith. The Umayyad Empire conquered an area stretching from South Asia across North Africa to Spain within a few generations. Seeing the possibility of losing most of their tax revenue, the Umayyads often simply refused to recognize Jews' and Christians' conversion to Islam as legitimate. Parsons points out that no more than 10 percent of the Persian population converted under the Umayyads, and the majority of Egyptians remained Christians into the ninth century.

As the Andalusians learned, Christians under Islamic rule face a powerful economic incentive to either convert or migrate. This steady erosion of the tax base, combined with the assimilation of the Muslim rulers into Iberian culture, weakened al-Andalus until it was reduced to the rump kingdom of Grenada and finally conquered by the combined kingdoms of Castile and Aragon in 1492—the same year Christopher Columbus set sail on a voyage that would allow Christian Spain to dominate the Americas for the next century.

The free market economist Julian Simon famously argued in his 1981 book The Ultimate Resource that a society's most important resource was not arable land, precious minerals, or energy supplies but the people who live within it. The decline of al-Andalus demonstrated that imperialists accepted this lesson long before economists. The major difference is that for Simon, it was people's ability to invent and adapt that makes them central to every economy, whereas empires see their subjects as sources of labor and tax revenue. The Spanish even referred to the Indians whom they forced to mine precious metals in South America as prendas con pies—"assets with feet." Nowhere was this fact more clear than in India under the British East India Company (EIC).

Empire building typically falls under the purview of governments, but in the 17th through 19th centuries, European states outsourced imperial conquest to quasi-private joint-stock companies. Governments granted these companies monopoly trading rights in distant regions and frequently offered their military might to ward off potential rivals. States rarely intended for the companies to become independent imperial powers, but the potential spoils of conquest proved hard for company officials to resist. After all, they had been freed from the discipline of competition, they were thousands of miles from political oversight, and their military risks were socialized by their state sponsors. As Bown points out in Merchant Kings, the EIC and similar corporations "were less the product of free-market capitalism than the commercial extension of European national wars and struggles for cultural and economic supremacy. They occupied the muddy grey zone that exists between government and enterprise."

The man most responsible for the East India Company's acquisitions in India was a young clerk named Robert Clive. In a foreshadowing detail, Bown relates that as a schoolboy, Clive organized a group of boys into a gang and extorted money from Shropshire merchants in exchange for "protection." Arriving in Madras in 1744, Clive was immediately thrust into a proxy war between the EIC and its French rival. He spent the next 13 years fighting the French company for monopoly trading rights in cities across the eastern coast of the subcontinent. Clive won a number of impressive victories, but the most portentous was a militarily unremarkable conflict in June 1757 at Plassey in the Bengal province of the splintering Mughal Empire. Clive defeated Siraj-ud-Daula—the nawab, or governor, of Bengal—in large part by bribing one of his commanders, Mir Jafar, with the promise of political office should Clive prevail. With victory at Plassey, Clive made Mir Jafar nawab of Bengal. More important, Clive and the EIC now held the right to collect taxes in the province, which, Parsons notes, already possessed an efficient, currency-based tax system from its centuries under different imperial masters. In effect, this made the EIC a part of the Mughal Empire, but as Mughal power continued to crumble, the company picked off various provinces. By 1765 it collected tax revenues in most of eastern India.

The EIC's primary concern was no longer trade but extracting revenue from its Indian subjects. The company made this explicit in an order quoted by Parsons: "Revenue is beyond all question the first object of Government, that on which all the rest depends, and to which everything should be made subsidiary." With tens of millions of revenue-generating subjects, the company's position would seem to be an enviable one, but Parsons observes that "the costs of maintaining a government and a standing army nearly bankrupted the Company. Clive's successors therefore had to squeeze the Bengali peasantry to remain solvent." Higher taxes produced tragic results for Bengalis in 1769 and 1770 when a famine struck the region. Unable to feed themselves and the EIC's insatiable appetite for riches, around 3 million people starved to death. News of the famine sent the price of EIC stock tumbling, and the British taxpayers bailed out investors with a £1.4 million loan from the Treasury.

The only people who seemed to profit from the empire were high-ranking company officials. According to Bown, when Clive returned to England in 1760 his fortune was so large that he did not even trust his own company to transport it. Instead, in a move that calls to mind Milo Minderbinder from Catch-22, he deposited hundreds of thousands of pounds with the rival Dutch East India Company in India and withdrew them once safe at home in England. But wealth did not translate into popularity. Bown writes that Clive "angered the people he had bested and the people whose fortunes had been stunted by his attempts to limit corruption. He angered people because he was arrogant and outspoken. There were many who would love to see him fall." Members of the aristocracy mocked the nouveau riche Clive as a "nabob," a derisive corruption of nawab. Clive also struggled with depression and an array of physical ailments, which he treated with opium. In 1772 Parliament launched an inquiry into corruption within the EIC. Clive was acquitted but sank deeper into depression, and in 1774, at the age of 49, he committed suicide by stabbing himself in the throat. Even for the profiteers, the blessings of empire were decidedly mixed.

Bown's chapter on the mining empire established by Cecil Rhodes in southern Africa provides an even starker example of an empire's failure to enrich its mother countries. Rhodes is best known among Americans today as the man who established the Rhodes scholarship at Oxford, but he was a commercial imperialist par excellence who helped found the De Beers diamond company, served as prime minister of the Cape Colony in what is now South Africa, and seized a territory that he "allowed" his colonists to name after him: Rhodesia. His territories contained the world's only large diamond mines and sizable gold deposits along with a population of thoroughly subjugated Africans to work them. Nevertheless, the British South Africa Company, which was responsible for the lands, could not turn a profit. Wars drained the company's revenues, and holding valuable land for white settlement required constant effort to keep Africans away from it. After years of little to no profit, the British government stripped the company of its powers and compensated shareholders with millions of pounds from the public purse.

Empire does not merely lack clear benefits for anyone outside of a small group of functionaries. Parsons argues that the spread of nationalism and of sprawling transnational identities such as Pan-Arabism have made it next to impossible to establish and maintain a modern-day empire. When identities were primarily local, successful empires could rule over vast territories inhabited by hundreds of different ethnic groups. With no common identity to unite subjects, the risk of mass rebellion remained low. But the European empires of the 18th and 19th centuries sowed the seeds of their own destruction, and the destruction of all traditional empires, when they spread the idea of nationalism to their subject peoples. Nationalism allowed rebellious imperial subjects to unite around a single cause, and it simultaneously robbed empires of the collaborators they had exploited for millennia. Whereas a respected first-century Briton could become Romanized without angering his neighbors, the French who assisted the Nazis in World War II were considered traitors to their own people. This development has not yet prevented powerful nations from trying to build new Romes.

Both Merchant Kings and The Rule of Empires are enjoyable, but they suffer from inverse problems. Merchant Kings is long on biographical detail but often short and misleading on historical context. For instance, Bown argues that in 1630 the Dutch colony of New Amsterdam (present-day New York) had fallen behind the English colonies of Virginia and New England in population in part because the English Civil War drove Puritans to seek refuge in America. The only problem is that the English Civil War did not start until 1642. By contrast, Parsons thoroughly contextualizes his arguments, perhaps to a fault. His narrative weaves between subject and ruler, colony and metropole, and spans thousands of years, so even knowledgeable readers will sometimes become lost in the procession of sultans, chiefs, and sepoys.

But these problems are relatively minor. Both books succeed in showing the small, concentrated benefits that empires bestow on a ruling class and the extraordinary burdens they impose on everyone else. The security and prosperity allegedly offered by empire is an illusion, and those societies that pursue it—even with the best of intentions—will ultimately receive neither. It's a lesson that could serve Americans well.

John Payne (johnwilliampayne@gmail.com) is a research assistant at the Show-Me Institute, a think tank in St. Louis.