Geography and environment often shaped but did not dictate outright the rise and history of the Mongol Empire. Political needs, military requirements, and the skills of particular individuals also contributed to specific developments and choices in Mongol policy. Determinists would assert that environmental factors did, in fact, dictate the course of events for the Mongol nomadic pastoral society, a challenging but untenable position when studying the 13th and 14th-century Mongol Empire.

Yet the Mongols inhabited a daunting environment. Their traditional territories were landlocked and so distant from an ocean as to block its moderating influence. They faced an extreme continental climate, with frigid temperatures and strong winds, creating extraordinary difficulties for a society. The short growing season and frequent summer droughts limited agriculture to a minuscule part of the land. Just 1 per cent of the land was suitable for agriculture, another 10 per cent had forests, and the remainder offered pasture and desert. The Gobi Desert was habitable, but its heat and aridity limited the population in this harsh terrain. The bulk of the population resided in the pasture lands north and west of the Gobi. Yet these rich grasslands frequently confronted the perilous zud, or severe winter snow and ice covers, which undermined the animals’ efforts to reach the life-preserving plants.

Relatively minor shifts in climate and temperature could create a crisis for the Mongol nomadic pastoral economy, which also relied, in part, on hunting, itself subject to similar problems with low temperatures and abundant snowfall. Even in recent times, bad winters have been devastating, leading to the death of more than 7 per cent of herds in some years.

Several scientific studies have documented a drop in mean annual temperature in north and central Mongolia in the period from around 1170 to the early 13th century and perhaps even later, a major factor in the history of the Mongols, especially under Genghis Khan. This sharp reduction generated the coldest climate in the region since 1500 BC. The ensuing decline in the growing season influenced the height and extent of the grasses, resulting in a devastating crisis for the Mongols. Proponents of this theory have asserted that the very survival of the Mongols demanded new social and political arrangements. Disunity and conflicts among the various Mongol and Turkic groups in the mid to late 12th century fomented chaotic conditions. However, wars and even battles could no longer be tolerated as a result of this ecological disaster. Unity and cessation of hostilities among the Mongols were required, offering Genghis the optimal circumstances to emerge as the leader of a powerful confederation.

This stimuli-response theory concerning temperature has merit, but it cannot be regarded as the sole explanation for Mongol unity under Genghis Khan. After all, precipitous declines in temperature had afflicted the pre-Mongol peoples of Mongolia, if perhaps not as severely as the crisis in the late 12th and early 13th centuries, yet unity had often eluded them. It has proven difficult to explain why, in such times of crisis, the earlier inhabitants of Mongolia and the Mongols themselves did not, as the 13th century Mongols did, solidify around a leader and then erupt from their lands to expand into other territories. As Gareth Jenkins observed in his paper, ‘A note on climatic cycles and the rise of Genghis Khan’, in a 1974 issue of the Central Asiatic Journal: ‘Objections against wholly mechanistic or deterministic arguments in which impersonal forces, such as weather changes, dictate the fate of nations are, of course, appropriate.’

Political and economic concerns were as critical as environmental and geographic factors in forging unity. As the Mongols fought among themselves in the late 12th century, non-Chinese peoples controlled north China and set up Chinese-style dynasties (with Chinese names for their dynasties). The Tanguts, a people related to Tibetans, dominated northwest China as the Xia dynasty, and the Jurchens, a group from Manchuria, ruled north China as the Jin dynasty. Both were powerful confederations and, on occasion, denied trade to the Mongols, who desperately needed the products of sedentary agricultural societies, especially after bad winters. Each also had commercial conflicts or tariff disputes with the Mongols. The Tanguts, for example, had imposed excessive tax demands on Mongol caravans traversing their territories, which lay along the major Silk Roads. Only a unified Mongol confederation could cope with such challenges, and this economic struggle with the Mongols’ neighbours was conducive to Genghis Khan’s rise to power. Political factors in his rise can also not be ignored. He faced powerful opponents in Mongolia, but he was a consummate diplomat and repeatedly worked out andas (or blood brotherhoods) with leaders of larger military forces. When he developed an equivalent or more potent army, he would often sever relations with his erstwhile allies and then attack them.

Genghis Khan’s other assets in his unification of the Mongols included his espousal of merit as the key to advancement. Abandoning the traditional Mongol practice of an aristocratic hierarchy, he selected and promoted men based on their performance, a policy that attracted the best individuals and facilitated his efforts at unity and at establishing the greatest confederation in Mongol history. His policy of proper division of the spoils from conquests, as opposed to demanding more for himself, bolstered his reputation and status among his people. In short, geopolitics, a true fusion of geography and environment and politics and economics, offers the optimal explanation for the unification of the Mongols in the late 12th and early 13th centuries and for the rise of Genghis Khan.

A group of scientists and a historian, originally associated with Columbia University, have recently presented ecological and geographic explanations for the Mongols’ creation of the largest contiguous land empire in world history, an empire which stretched from Korea to Russia in the north and from southern China to Syria in the south. Like the proponents of the decline in temperature theory, the Columbia scientists state that the Mongol economy was sensitive to climate change, with significant snowfall or drought having a dramatic impact on the population. They suggest that preliminary findings from the study of tree rings, mostly in central and southern Mongolia, indicate that the period from 1211 to 1225 was wet, which resulted in more and lusher pastures. In turn, the abundance of pasture permitted an increase in the size of the herds. The number of horses, which were essential for the cavalry and thus the Mongols’ main military asset, grew, and the ruler thus had the ability to engage in military campaigns beyond Mongolia. More animals and the development of some agriculture, facilitated by the increased moisture, yielded a reliable and greater food supply, which could sustain a larger population. More people, in turn, meant a larger military force, which could capitalise on the increased availability of steeds. Moreover, a growing population required the greater political centralisation Genghis Khan provided. Unity, food surpluses, and more horses (the engines of war) allowed forays into China.

The theory of climate change offers insights into the forces that facilitated the Mongols’ campaigns and expansion, but it fails to explain the Mongols’ motivations in emerging from Mongolia. It certainly assists in understanding the Mongols’ successes, but it is not the whole story. In the absence of written sources, such investigations, together with studies in archaeology and material culture, provide glimpses of the realities of 13th-century Mongolia. This interpretation may reveal clues about conditions in Mongolia, yet it does not yield much insight about the incentives for the Mongols’ explosion from Mongolia. Trade disputes with non-Chinese dynasties in north and northwest China and Genghis Khan’s ambition, allegedly fuelled by the sky god Tengri’s instruction to bring the world under one sword, supply appropriate rationales for the foreign military campaigns. The increased size of the army also almost inexorably created demands for further conquest and booty. After all, how could Genghis Khan maintain the army without additional conquests?

Yet difficulties intrude on this climate change theory, even in ecological terms. The greater rainfall and higher precipitation in Mongolia may not have been replicated in north and northwest China, the regions of Genghis Khan’s first two campaigns. Did climate change also occur in these regions in China and provide the abundant grass that the horses allegedly had available in Mongolia? For instance, the Mongols campaigned in north China for four years, from 1211 to 1215, and thus had to rely on the pastures in the region. The proponents of the theory have not established that equivalent climate change also took hold in north China. The question therefore arises as to whether the length of the campaign would have required the Mongol forces to return to Mongolia for the lush vegetation their horses needed, before renewing their offensive in the north. Still another challenge to the theory is that horses were not as critical in the campaigns in north and northwest China. Since the Mongol forces had to breach the defences of walled and populated cities, such siege engines as catapults and mangonels were needed. These engines battered the inhabitants and finally ended in the locals’ defeat. Were horses and abundant pastures as significant in these Mongol victories?

Just as important in Mongol military success was the weakness and disunity that prevailed in much of Asia. Three separate dynasties ruled China; the Abbasid Caliphate in Baghdad was declining; and Russia was composed of independent cities with no unified state. The Mongols, with horses alone, even well-fed steeds, would not have overwhelmed Asia if China, Russia, and the Middle East were each united. Again, a variety of factors, not simply the environment, accounts for the Mongols’ spectacular advances.

A more difficult environmental issue that has not been satisfactorily explained concerns Genghis Khan’s third foreign campaign. The Central Asian government of the Khwarazm Shah had killed Turkic and Mongol members of a caravan and then executed the envoy Genghis Khan had sent to demand that the official responsible for the murders be turned over to the Mongols. Because the Mongols considered the killing or harming of an ambassador to be the most heinous of crimes, Genghis Khan was compelled to organise a punitive expedition. Contemporary sources assert that he gathered a force of some 200,000 men for this campaign. Each Mongol soldier travelled with four to five horses on such expeditions – one or two were ridden, two carried supplies and food, and one would be fresh and ready for combat. The total would have amounted to an astounding 800,000 to 1 million steeds. It is true that the Chinese and Persian sources exaggerate numbers. Nonetheless, the consensus of scholars is that at least 100,000 men set forth.

This campaign was the most far-flung of Genghis Khan’s expeditions. The Mongols were somewhat north of and relatively close to the Tanguts and the Jurchens, their prominent and earlier enemies. Central Asia was distant and required travel through daunting deserts and lofty mountains. Desert brush would seem to be insufficient sustenance for nearly half a million horses. Unlike camels, which can withstand days without food and water once replenished at oases or towns, horses need extensive daily foraging as well as considerable amounts of liquid. The environment through which the Mongols travelled was harsh and unforgiving, with some regions having scarce plant life or potable water, and the distances from one oasis or town to another were often substantial. So how did the Mongols obtain sufficient grass and water for their horses? This question remains a mystery and contributes to views of the Mongols’ peculiar closeness to the natural environment and their ability to adjust to new surroundings.

The environment and the Mongols’ adaptation to it were crucial issue in this expedition. Yet the nature of the Mongols’ adjustment to the daunting desert and mountains remains elusive. Politics, economics, and charismatic leaders are scant use in explaining how such logistical difficulties might have been overcome. Genghis Khan spent six years in Central Asia. Supply lines had to be set up before each movement forward; the Mongols had to be sure that their horses would have sufficient grass and water to reach the next battleground, usually an oasis or such established cities as Samarkand and Bukhara. But despite these precautions, Mongol casualties were much greater than in Genghis Khan’s earlier campaigns. It is thus no accident that the Central Asian towns were the first locations in which Mongol troops remained behind as occupying forces. Genghis Khan had not occupied the Tangut or Jurchen domains. He had extracted economic privileges and then he and his forces had returned to their homeland. The logistical and environmental problems of having to undertake another campaign in Central Asia, if the native inhabitants challenged Mongol demands on trade, taxation, and recruitment of men for other expeditions, dictated tight control and occupation were necessary to avoid the great expense and substantial loss of soldiers and horses that a second campaign would entail. In this case, it was the environment, alongside what can be labelled geopolitics, that determined the Mongols’ objectives and strategy.

One of the most controversial geopolitical issues concerning the Mongol expansion is their sudden withdrawal from Hungary in 1242. Batu, Genghis Khan’s grandson and eventually the founder of the Golden Horde in the new Russian capital in Sarai, had initiated a campaign against the inhabitants of Russia and eventually laid siege to and occupied the major city-state of Kiev on December 6, 1240. Because the regional ruler Alexander Nevsky made peace with the invading force and permitted the Mongols to trade with his city of Novgorod, the Mongols did not attack his domain and, instead, Batu headed south for a two-pronged assault on eastern Europe. One army headed toward Poland and faced little resistance in conquering Sandomir and Cracow. Then Duke Henry of Silesia confronted the Mongols near the town of Legnica (or Liegnitz) on April 9, 1241. His forces had planned on hand-to-hand combat, but the Mongol archers initiated a devastating attack, and their arrows won the day; Henry himself died during the battle. Two days later, Batu overwhelmed the army of King Béla IV of Hungary at Muhi, and by December had moved into Budapest. Then, just as suddenly as they had appeared in Europe, Batu and his army withdrew from Hungary early in 1242.

Uncertainty surrounds the reasons for this withdrawal and the abandonment of possible incursions into western Europe. One theory is that the death of the Great Khan Ögödei (who ruled from 1229–41) prompted the retreat. Mongol succession practices mandated a call for the nobility to meet in a convention (or so-called khuriltai) in Mongolia to select a new leader, who had to be one of Genghis Khan’s descendants. Batu left Europe but did not return to Mongolia because he had learned about the succession struggle and thought he could exert more influence from outside his homeland. A second, political motive may have been that Batu’s principal objective had always been to punish King Béla for killing one of his envoys. Once he had achieved this goal, he had no interest in capitalising on his victory. A third explanation focuses on the losses the Mongols had suffered in Poland and Hungary, and they feared that they might encounter a larger western European force when they needed to recover from their campaigns in eastern Europe. Verification of this explanation is impossible because it would require knowledge of what was going on in the minds of Batu and his commanders.

An environmental explanation for Batu’s withdrawal is the possible lack of pasture, as the Hungarian grasslands may have been depleted by the sizeable influx of animals. The climate change theorists have supplemented and introduced a variation to this hypothesis. Based mostly on literary testimony and on somewhat ambiguous ecological evidence, they postulate an alarmingly cold winter in 1241–42 in Hungary, with drops in temperature, early frost, and considerable snowfall. The growing season was cut short, leaving scant pasture and putting the lives of the large number of horses at risk. A sudden rise in temperature in the early spring of 1242 caused the snow to melt and create a muddy terrain inhospitable to the animals. In addition, many inhabitants, learning of the Mongols’ movement toward their territory, had fled, and the land lay fallow. Mongol soldiers who often depended on food in enemy territory could not survive on local supplies. They could not remain as an occupation force. The southern Russian steppes, with their lush pastures, beckoned, and Batu led his forces to these inviting surroundings. They were fortunate to do so because literary sources cite a famine in 1242 and even a proliferation of wild beasts, in particular wolves, who attacked humans.

This attractive climate change hypothesis is based on several suppositions. The literary sources may have exaggerated the severity of the cold weather, as well as the lack of pasture for horses and agricultural produce for their masters. The tree ring evidence in Hungary is not clear, and while other ecological records do often suggest prevailing lower temperatures, not all of them do so. More research in Hungary and eastern Europe is needed. This kind of environmental study in these regions is at an early stage of development. Nonetheless, the combination of the depleted grasslands, due to the vast herds of Mongol horses, and the strong possibility of unusually low temperatures may have contributed to Batu’s exodus from eastern Europe.

Some historians assert that geography played a role in the collapse of the Mongol Empire. They argue that the empire was simply too large to be readily governed by a formerly nomadic pastoral group with no experience of controlling such an extensive territory. In fact, within 15 years of Genghis Khan’s death, the empire split into four segments, each with virtually independent khans – East Asia, Central Asia, the Golden Horde in Russia, and the Middle East.

This is certainly a plausible explanation, but two specific and uniquely political factors played their roles in the demise of the Mongol Empire. The Mongols never did devise a regular and orderly system of succession. A khuriltai, or assembly of the Mongol nobility, chose the next Great Khan, setting the stage for succession struggles and eventually civil wars. The second problem arose as some Mongols began to identify with the sedentary civilisations they had subjugated and ruled. Mongols in China adopted Chinese political institutions and rituals, and in Persia some converted to Islam. Mongols who espoused the traditional ways and the Mongol heritage started to oppose the Sinicised and Persianised Mongols, leading to splits and weakening both. Geography alone did not cause the collapse of the Mongol Empire: political factors were significant as well.

In sum, the environment certainly influenced the rise, development, and growth of the Mongol Empire, but a variety of political, economic, and social factors were essential components. Specific individuals, including Genghis Khan and his descendants – and their custom of leadership succession and the other policies they created – also shaped the Mongols’ trajectory in forging one of the world’s largest ever empires. Careful scientific studies of the physical environment will, in future, contribute to a fuller understanding of its impact on Mongol history and clarify the significance of geopolitics in its remarkable record.

This essay originally appeared under the title ‘Geopolitics and the Mongol Empire’ in ‘The Return of Geopolitics: Perspectives from the Engelsberg Seminar’, Bokförlaget Stolpe, in collaboration with Axel and Margaret Ax:son Johnson Foundation, 2016.