Because immigration played no small part in the demise of Rome. The period from the late-4th century to the mid-6th is frequently even termed “the Migration Period” or, in the more thunderous German, the Völkerwanderung. That long century was shaped the new ethnic groups that moved into the Empire from central and eastern Europe, spurred on by an initial exodus of population from the Eurasian steppe. The exact causes of this exodus — climate change, overpopulation, the building of the Great Wall of China — are ceaselessly debated by historians. But by 500 AD, with Anglo-Saxons north of the Channel, and Vandals, Franks, Goths further south, the vast majority of the ex-imperial landmass was ruled by newly arrived dynasts and warrior groupings.

For some modern commentators, however — from Boris Johnson to Pat Buchanan — the history does not stop there, and there is an immediate modern parallel. If, they argue, the United States and its Western allies represent something like a new empire, it too is threatened with invasion by incoming migrant hordes. And they see these hordes most visibly in the vast migration of peoples currently taking place across America’s southern border with Mexico, and through the Mediterranean world from North Africa.

But, while the historical comparison between Rome and the West has an attractive simplicity, there are fundamental disanalogies. Rome’s economy was overwhelmingly agricultural, and steady-state. Its GDP could not increase in anything but the very long term, since the stock of good land was fixed and farming methods slow to improve. Therefore the establishment of the Western successor states necessitated the partial or sometimes total (as in southern Britain) confiscations of wealth-generating agricultural assets from their existing owners to support their new rulers. In other words, migrants did literally and materially displace the Romans.

In comparison, wealth generation in the West — which is neither steady-state nor agricultural — has become effectively dependent on flows of migrant labour. Since 1900, average family sizes have declined dramatically across the developed world: currently only Iceland and Israel are producing the canonical 2.1 average children per adult female for the current population to reproduce itself in the next generation. Everywhere else, birth rates are below this level and in some cases — particularly Germany, Hungary, and Japan — far below. Therefore, immigrants aren’t appropriating wealth from the West, but supplementing a shortfall in the productive workforce. Which is why every 1% increase in legal migrant numbers — and the overwhelming majority of migrants into the west do arrive legally — adds an average 2% to GDP in Western countries, and average unemployment rates have not increased despite all the recent population inflows.

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But, if we expand the discussion of modern migration to include its non-Western dimensions, a different comparison with Rome offers another, much more compelling parallel. Because the obsessive media coverage of Mexico and the Mediterranean refugee crises actually elides the most important modern migration story of them all. Apart from those arriving in the West, many times more people (countless millions in fact) have been on the move within the developing world. It is this new age of migration, the largest movement of people in the entirety of human history, which poses the real challenge to continued Western economic prosperity.

It began as a by-product of colonial-era economic development in the 19th century. As the rapidly industrialising West’s demand for raw materials from its colonial territories grew, as well as for foodstuffs for its expanding urban populations, new networks of connection grew up across the different empires: based on ports, internal river systems, and, eventually, railways. Former subsistence peasant producers across Asia, Africa, the Caribbean and South America found themselves sucked into these networks in ever-increasing numbers to provide the labour for new cash crops, raw material production, and to establish and run the transport networks.

The process only accelerated under the newly independent governments of ex-imperial territories in the years after 1945. Many devoted considerable resources to basic education, attempting to create homegrown industrial bases to fend off expensive imports from their former masters. And this sucked people in massive numbers from continental interiors to congregate in coastal cities such as Shenzhen, São Paolo, Lagos, and Mumbai. Once there, better healthcare and a plentiful food supply added exponential population growth into the mix.

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In economic terms, these import replacement strategies enjoyed only limited success, and largely failed after the oil price shocks of the Seventies. But what this astonishing flow of humanity did achieve was to put in place a ready-made labour force across different parts of the developing world for the Eighties, when Western countries lifted their long-standing capital controls. As the West deindustrialised, investment began flowing outwards to the developing world, where labour was so much cheaper, with the aim of returning Western corporations — and hence the West as a whole — to post-war levels of growth.  

This worked, for a time. But over subsequent decades, Western investment has combined with the emergence of new classes of indigenous entrepreneurs to generate a global shift in the geographical location of manufactured wealth production. Since 1947, for instance, the population of Bangalore has increased from 700,000 to about 14 million, the vast majority supported by manufacturing jobs, while India’s national literacy rate has risen from about 20% to 75%. Over the same period, by contrast, London’s population has stayed more or less the same and it has ceased to be a major manufacturing centre. This second Völkerwanderung had created such a cost-effective labour force that it proved overwhelmingly logical, as globalisation gathered momentum, to relocate a huge percentage of global industrial production away from the West’s old manufacturing centres to the teeming new coastal metropoles of the developing world.

The process is irreversible, and far from complete. Public attention focuses on China and the other Bric countries, but seven of the world’s 10 fastest-growing economies are now African. Kenya, for example, is still mostly famous for its tea and game reserves. But it currently enjoys an annual growth rate of over 7% and Nairobi has become a digital finance hub. And it is in examining the peripheries of the Western world’s old empires, that the comparison with Late Antiquity achieves a new resonance. Imperial systems first come into existence with the purpose of enriching the population at the imperial centre. But over the longer term, they unintentionally kickstart revolutionary processes of economic and hence socio-political change around their fringes, and eventually the emergence of new entities capable of challenging the Empire’s continued dominance.

In the Roman case, 400 years of sustained economic demand for foodstuffs and other raw materials from across the Rhine and the Danube generated a discernible agricultural revolution. By the end of it, barbarians could support themselves in large enough numbers to swarm in on the eve of the Empire’s collapse. Over the same time frame, diplomatic subsidies and the fostering of apparent allies simultaneously produced larger and more coherent political superstructures at the head of these populations. In the 5th century, therefore, the ancient Roman West was carved up by immigrant-warrior groups whose greater size and coherence were the direct result of centuries of coexistence with imperial power. And this is where our own real parallels with Roman history lie. The old global dominance of the modern West is now being challenged by new actors whose growing economic strength — the foundation of their emerging political clout — is the end result of development processes that were originally set in motion to further Western interests.

The outcome of Rome’s imperial lifecycle was always likely to be dismemberment. The outcome for the modern West need not be so catastrophic. There will be enormous political challenges: in Ukraine and the developing sabre rattling over Taiwan new actors are already testing the actual strength and moral resolve of the old Western Empire, and no doubt there are other tests to come. But the vast majority of the developing modern periphery is showing not the slightest desire (or indeed need) to invade the old imperial core in search of greater wealth.

There are other difficulties to overcome — not least pollution and climate change — but the stock of wealth-generating assets is not so limited, and, in principle, there can be sufficient economic growth to satisfy the rest of the world’s legitimate demands for a reasonable share of global GDP, while preserving plenty of wealth for the West. The outcome of the modern Volkerwanderung need not be so much the end the end of Empire, but a diffusion in the distribution of global wealth, Western hegemony fading with a whimper, not a bang.

This is the nearly 400-page case Marie Favereau lays out in The Horde: How the Mongols Changed the World — and it’s a convincing one. A professor of history at Paris Nanterre University, Favereau’s previous published work focused on the wide-ranging geopolitical connections the Mongols made, and subtle cultural revolution that transformed them from an alien, conquering elite to deeply-rooted imperial administrators who shaped the societies they ruled. Though Favereau occasionally fixates excessively on the internecine dramas of Genghis Khan’s family, on the whole The Horde is both brisk and dense with facts and analysis about a period and people that remain unknown to most Westerners.

The Golden Horde emerged during the Pax Mongolica, when the various divisions of the Mongol Empire — Khanates —were ruled separately by the descendants of Genghis Khan, but united by treaties based on Mongol tradition. Marco Polo traversed the length of Eurasia, from Europe to China, and back, when the Mongol Empire was at its peak in the late 13th century. But the Golden Horde was the most geographically expansive of the Khanates. It stretched from modern Bulgaria and Romania in the west, to the vast Eurasian steppe north of the Black Sea, and yet further eastward still to the western edge of Mongolia. Beyond it lay the Great Yuan, who ruled most of the landmass of China and Mongolia, while the modern Middle East and southern Central Asia were under the two smaller Khanates.

The high noon of the Golden Horde’s power came between 1250 and 1400 AD, when it had unquestioned hegemony over all of the Russian principalities, northern Central Asia, Siberia and the Caucasus (Moscow remained a nominal vassal of the Horde until 1480 AD). This was an empire at enormous scale, with a vast reach — like Augustan Rome, or Spain during el Siglo de Oro, or Victorian Britain. For centuries, the Golden Horde stood athwart the trade routes of Eurasia. It was colossal.

But before there was the Horde, there were the four sons of Genghis Khan: Jochi, Chagatai, Ogedei and Tolui. It was from Jochi that the Horde would come. The eldest, he had a checkered relationship with his father, and with good reason. His mother, Börte, had been kidnapped by an enemy of Genghis Khan eight months before his birth. Although a shadow was cast over Jochi’s paternity, Genghis claimed him anyway. (Favereau straightforwardly accepts that Jochi was likely not Genghis Khan’s biological son.) After a great conference of Mongol leaders in Central Asia was held to determine the succession, and passed over Jochi, he marched his forces west, pitching his tents on the far fringe of the Mongol Empire north of the Caspian Sea.

Jochi’s self-exile set in motion a long train of consequences, and the real narrative of The Horde begins with Jochi’s sons, Orda, Batu, and Berke. Their lives illustrate three principles that reoccur again and again in The Horde. First, there is the principle of consensus and coexistence. Batu ruled the western half of the Golden Horde, while Orda ruled the east. These were the Blue and White Hordes, due to the association of these colours with the west and the east, and for over a century they respected each other’s territory. Second, the ascension of the younger Batu over Orda as Khan reversed expectation and reflected pragmatism.

Rather than slavishly following rules and customs, the Golden Horde embraced flexibility in its culture and political organisation. Finally, after the death of Batu, the youngest brother, Berke, became the Khan. Berke was the son of a Muslim woman, and he eventually converted to Islam, anticipating the later wholesale conversion of the Horde’s Mongol elite. Berke’s religious choice was also reflected in his geopolitical decision-making: he had no compunction about aligning with fellow Muslims against other Mongols. But Berke was also a pragmatist, not a fanatic, and he valued Mongol legal precedent and accepted the importance of religious toleration within his empire. The Golden Horde eventually became Muslim, but the empire it dominated was never Islamic.

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One of the major themes of The Horde is that the wealth of the ruling class of the Golden Horde was uniquely fuelled by trade, and this drove much of its diplomacy and war-making. Unlike China, Europe or the Near East, the territories of the Horde were sparsely populated. The Khans of the Golden Horde could not tax vast numbers of peasants to sustain their wealth. Rather, their economic activity was geared toward exploiting natural resources, as with furs shipped to Europe via the Hanseatic League, and customs collected on overland trade passing between Europe and China, as well as exports of slaves south to Egypt via Constantinople.

Some actions of the Khans that seem ideological on their surface turn out to have straightforward material explanations. Berke’s conversion to Islam cemented an alliance with the Mamluk regime in Egypt against the Mongol Il-Khanate. The Golden Horde supplied the Egyptians with slave soldiers to battle their Il-Khanate cousins, resulting in the first major defeat of the Mongols, which stopped their military advance. But those slave soldiers were also a major economic commodity that powered the financial health of the Golden Horde. The conflict with the Il-Khanate was not just ideological or geopolitical, but driven by the reality that the Golden Horde’s trade routes were constantly threatened by enemies — in this case, other Khanates. Berke and the Khans who succeeded him were engaging in literal trade wars.

Similarly, the amity between the two major divisions with the Horde, the Blue and the White, was not just a matter of sentimental familial bonds between the descendents of the brothers Batu and Orda. It reflected business savvy. The Golden Horde invested heavily in a Silk Road route that began at ports on the Black Sea, like the Genoese colony of Kaffa. The route continued eastward, grazing the southern fringe of Siberia, and moving onward all the way to the rich lands of the Great Yuan (Mongol-ruled China).

Cooperation between the Blue and White Hordes was necessary, not simply preferred, for this Silk Road to function. Additionally, propagandists in the service of the Horde whispered in the ears of merchant houses in Europe that the southern route that snaked through the rugged lands of the Il-Khanate was more dangerous and expensive. The ruling class of the Golden Horde wanted the world to know they were “open for business,” and offered a favourable tax regime for merchants willing to traverse their peaceful and well-ordered territories.

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But trade-fuelled prosperity is subject to the vicissitudes of globalisation. The collapse of the Il-Khanate in the 1330s resulted in the northern route achieving even greater prominence, as the southern Silk Road fractured between numerous hostile states. This monopoly was short-lived. In 1368, the great engine of west-east trade was turned off; the Mongols were expelled from China, and the ascendent Ming Dynasty shut the door to the rest of the world. If agriculturally-based empires were vulnerable to weakening in times of famine, merchant prince fortunes soared at the pleasure and caprice of foreign potentates.

Additionally, the 14th century saw the lucrative global trade in furs across the lands of the Horde facilitate the spread of the Black Death to Europe and the Near East from the eastern steppe. As we keenly feel today, one downside of globalisation is that a much larger human population can be a potential host for a pandemic. More than 30% of Europe and the Near East died from the bubonic plague, and the impact was significant on the Horde itself, as some of its leaders succumbed to the disease. The paradoxes and discontents that emerge from globalisation are long-standing.

Favereau’s narrative makes much of the reality that the Golden Horde was religiously pluralistic, a phenomenon immediately intelligible to contemporary readers. This was a legacy of Genghis Khan himself, who exempted clerics from taxation and left all houses of worship intact. He believed that the sky god, Tengri, had given him the world. Genghis and his descendants looked favourably upon all religions as the expression of the same divine principle.  Most earlier Khans were not Muslim, but devotees of Tengri. Nevertheless, they patronised Islam, Buddhism, and Christianity to cultivate relationships with subject people, most of whom were Christian or Muslim, and encourage the migration of other Mongols, many of whom were Buddhist. However, 1313, the Khan of the Golden Horde declared Islam the religion of the Mongols in the Blue and White Hordes.

Even after the Khan of the Golden Horde demanded that Mongols in his domain convert to Islam, he continued to encourage Christians to practise their religion (in contrast, Buddhist Mongols were expelled and their temples torn down). The Golden Horde exempted Russian Orthodox Church lands from taxation and encouraged European Roman Catholics in the trading cities to build their own houses of worship. Even when the Mongol ruling class became thoroughly Islamicised, they accepted religious diversity for both principle and profit.

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Though the global commercial orientation and religious tolerance of the Mongols are nothing to sneeze at, perhaps the biggest direct impact of the Golden Horde was upon the nascent identities of their subjects. Almost as an aside, Favereau notes that the Mongols liberated Wallachia from its nomadic overlords, laying down the foundation for modern Romania in the 13th century. But this is nothing, compared to how the Golden Horde played inadvertent midwife to the rise of the modern Russian state. Traditional accounts date the origin of Russia to the Christianisation of Kievan Rus’ under Vladimir the Great at the end of the 10th century. Though 1,000 years later this culture and society may seem exotic to us, Kievan Rus’ was oriented to the west and Europe, which explains how Anne of Kiev became queen of France in 1051. The deep separation between Russian culture and that of Western Europe only emerged during the period under the Golden Horde, as the ruling elite shifted its focus from Kiev in the west to Moscow in the east.

By the time the Mongols arrived, the Rus were ruled by a patchwork of more than a dozen principalities. Their main southern trading partner, the Byzantine Empire, was in sharp decline, and the Northern Crusades by German knights were impinging upon the prosperity of the Baltic-facing trading cities. The Mongol invasion was even more traumatic. In 1246, an envoy of the Pope traveled through Kiev and observed that “it has been reduced almost to nothing, for there are at the present time scarce two hundred houses.” The only major city to avoid being sacked by the Horde was Novgorod in the far north, which survived through preemptive surrender.

Modern Russia was built upon the ashes of cities the Mongols burned. The imperial Russian state of Ivan of the Terrible that rose to unprecedented power in the 16th century was not shaped by Kievan Rus. It did not face the European kingdoms to the west, but the Golden Horde to the east. Instead the rulers of Moscow were positioned between the core territories of the Rus to the west and the lands of their steppe rulers to the southeast. A perfect location to be cultural and geopolitical go-betweens.

Just as Batu had been promoted over Orda, so the Khans of the Golden Horde strategically promoted Moscow’s junior princely lineage, the Danilovich, above the others. The House of Moscow did not have the pedigree, but they got the job done, collecting revenue and suppressing revolts. In the process, Moscow accrued enormous power and influence, eventually overthrowing the “Tatar Yoke” to impose its own domination on what became imperial Russia. While 11th-century France obtained a queen from Kiev, 18th-century French asserted that if you “scratch a Russian… you find a Tartar.”

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Favereau’s contention that you cannot understand the Russian imperial order without considering the formative impact of the Golden Horde is just one aspect of her argument. A broader thesis explicit in The Horde is that the empires that arose in the last 500 years mimicked and adapted many of the features of the steppe polities they dismembered. Russian historiography speaks of the period of subordination to the Golden Horde, but the centuries of disgrace were erased only with the conquest of the lands of their erstwhile oppressors: Siberia and Central Asia.

The Russian Empire also assimilated the Horde’s ruling class. Much of the Mongol military elite became Christian and part of the Russian nobility, while Jochid princesses married into the Russian ruling houses. A tradition of autocratic rule arose that was different from the more decentralised model that had characterised Kievan Rus. Ivan the Terrible took the title Tsar only in 1547. Before that he had simply been a prince, a reflection of the Kievan legacy. His assertion that he was a Tsar reflected an imperial ambition more in keeping with the traditions of the steppe than the nation-states emerging in Western Europe.

Though there are occasions in Favereau’s narrative where fixation on the political and social intrigues of the Jochid lineage overshadow the broader lessons, The Horde is most deeply understood as a cultural and social history. Like many histories which centre the steppe, it attempts to roll back the erasure of nomadic empires from the genealogy of modern states and societies. This process is clearest in the case of Russia, but applies pervasively across Eurasian history.

Historians of the steppe observe that the kingdoms of Europe and the emirates of the Near East may have built vast stone cities which withstand the test of time, but the religious tolerance and the global mercantile orientation of the Mongols are much more in keeping with the values of modern cultures. Like the Horde, modern developed societies are not fundamentally agricultural.

Also like the Horde, modern developed societies tolerate a wide variety of religions, often with the unspoken understanding that this will be socially useful. And, like the Horde, modern nation-states tend to exhibit a centralising and expansive tendency, with an explicit hierarchy of administrators and decision-makers. The Horde argues that multicultural global empires have much more relevant lessons for modern nation-states than the agrarian societies which the Mongols ruled. Without recognising it, we all still travel on a path the Mongols carved out for us centuries ago.