A fan-wide assessment of modern depositional processes on the Río Grande (Guapay) megafan, coupled with the analysis of its Holocene evolution, reveals that most of the 36,000 km2 megafan surface has been subject to sedimentation processes and/or reworking in the last 6–7 ka. Today, depositional dynamics as inferred from multi-date satellite imagery are mostly restricted to a ~ 2,000 km2 depozone on the distal megafan, and are characterised by avulsive fluvial environments. Combining remote sensing with field observations and geochronology at key locations has allowed to capture links between the dynamics of depositional processes and larger-scale landforms, documenting significant changes in the location of the depozone since ~ 4 ka. On shorter time scales, the human impact on these dynamic sedimentary processes is expressed by artificial levees and re-channelisation following crevasse splays. This is likely to have prevented a number of channel avulsions over the last decades and implies that the use of modern avulsion frequencies and depositional rates alone as analogues for understanding Holocene megafan evolution is of limited use. Instead, our observations emphasise the increasing vulnerability to future avulsion events within an intrinsically unstable fluvial environment that has seen rapid deforestation and population growth in recent time.

When Temüjin, the man who became Chinggis Khan, was born, the Mongols were but one of several groups vying to power. Shattered both militarily and politically by the Jin Empire and Tatars in the 1160s, the Mongols lacked a khan to unify them. Most of what we know of Chinggis Khan's early life comes from one of the few Mongol sources related to the Mongol Empire: The Secret History of the Mongols.11 The general narrative that follows is taken from the Secret History.

Temüjin's Rise to Power

Temüjin's rise to power faced many obstacles. Yesügei, murdered when Temüjin was approximately nine years old, had proven to be a strong military leader although he was not a khan. With his death, most of Yesügei's nökhöd (sworn companions) abandoned his family and sought service with more promising leaders, including the rival Tayichi’ud clan. Hö’elün, Temüjin's mother attempted to hold the family together but also faced the challenge of raising her sons alone, a difficult task given a developing rivalry between Temüjin and his elder brother, Bekhter (the son of Yesügei's second wife). Despite their dire circumstances, lacking flocks of sheep and possessing few horses, Temüjin murdered Bekhter as the latter stole food from Temüjin and his brother Jochi Qasar

Temüjin also spent an indeterminate time as a captive and perhaps slave amongst the Tayichi’ud. This may have been for his crime of fratricide or perhaps simply as a method to reduce any prestige that Yesügei's family may have still held. He eventually escaped and began to restore the fortunes of his family. Shortly before his father's death, Temüjin had been betrothed to Börte, the daughter of Dei Sechen of the Onggirad who saw something promising in Temüjin. Dei Sechen told Yesügei,

Dei Sechen was indeed correct about Temüjin, even if it took years before his auspicious nature became apparent to others. Now married, Temüjin then used her wedding dowry to secure the protection and patronage of Toghril, Khan of the powerful Kereit confederation in central Mongolia.

The Mongol Empire marks the transition from the medieval world to the modern world. The post-Mongol world looked considerably different from when the Mongols first arrived on history's stage. This change included not only the political map of Europe, but also in terms of religion, culture, technology, and ideas are part of what I term the Chinggis Exchange. This diffusion had an impact in world history similar to Alfred Crosby's Columbian Exchange, albeit perhaps more subtle. This impact can be seen in political geography, the religious map of the world, and trade and information networks across Eurasia and beyond.

The Impact on Political Geography Today

Starting with the political geography, the most notable change brought about by the Mongol Empire occurred in China. Rather than three empires, there was only one, the Ming Empire. The Ming Empire benefitted greatly from the Mongol Empire and in many ways can truly be considered a successor state, particularly in the early decades of its existence. The Ming Empire was notable for the inclusion of Yunnan (the former kingdom of Dali), which had previously never been part of a Chinese state. In the north, there was Mongolia—it was not simply the steppes, but viewed distinctly as the home of the Mongols, who were ruled by Chinggisid khans. Although they briefly experienced unity under Dayan Khan, the Mongols once again fractured into a number of “tribes.” The border, which fluctuated considerably, became fixed as the Ming constructed the Great Wall at huge cost. While the wall served as a defence against the Mongols, it was also intended to prevent Chinese from escaping to the freedom of the steppes as well as to demarcate the extent of Chinese territory.

In Central Asia, by the sixteenth century the Uzbeks moved into Māwarānnahr and occupied what would become, in the twentieth century, Uzbekistan. In the meantime, their empire fragmented into a number of small states known variously as the Emirates or Khanates of Bukhara, Khiva, and Kokand. These lasted until their conquest by the Russian Empire in the nineteenth century. Further north, the Kazakh Khanate formed. It too fragmented into three separate polities due to internal issues as well as external pressure from the Oirats and then later from the Zhungar Empire

A quick glance at the world map clearly indicates that the Mongol Empire no longer exists. Yet when did it end? The last Chinggisid ruler abdicated his throne in Khiva in 1920. Yet, one could hardly say the Khanate of Khiva was the last edifice of the Mongol Empire? Do we take 1260 as the end of empire, after the death of Möngke and the beginning of the civil war between Ariq Böke and Qubilai? As we’ve seen, this war did not strengthen the empire but fractured it into four or five separate states, with Qubilai's Yuan Empire having only a hypothetical sovereignty over the others. Or do we end it in 1305 with the end of the Pax Mongolica? As the Da Yuan Empire in East Asia was seen (at least by its rulers) as simply a Chinese term for the Yeke Monggol Ulus, do we assign the end of the empire to 1368 when the Mongols were driven out of China or in 1388, when the Northern Yuan ended?88 Yet, the Jochid Ulus and Chaghatayids continued to rule, but even they did not end with a clear expiration date. Indeed, one can argue that the Mongol Empire never fell—it was never toppled by outside forces or natural disaster. Rather, it just faded away, slowly dissolving as a series of successor states emerged in its former territories as the Chinggisids gradually lost real authority even while their charisma still lingered.

In 1256, there was no reason to think the Mongol Empire would end. Not only were the Mongol armies once again on the move, but their ruler, Möngke was energetic—not only did he have a solid military reputation, but he also aggres sively reformed the administration of the empire, rooting out corruption and increasing the centralization of the state. Indeed, his policies should have ensured the continuation of the empire rather than initiate its decline. Unfortunately, the seeds for the dissolution of the empire had been planted long before the Toluid Revolution and Möngke's reign.

As with the success of the Mongols, there is no single reason for its demise. Problems with succession, territorial issues, environmental factors, religion, disease, and the failure of Chinggis Khan's meritocratic system all factored into the decline of the Mongols.

It was a dark and stormy night when the Mongol fleets anchored off the coast of Japan at Hakata Bay and Imari Bay in 1281. With their fleet arranged as a floating fortress, the Mongols waited for a dawn that never came as a tsunami struck the Mongol fleet, destroying much of the fleet and scattering the remainder. The failure at Japan marked a tipping point for the Mongols. No longer did their armies march inexorably across Eurasia defeating all who opposed them, creating an empire that stretched from the shores of Korea to Bulgaria. Even after the dissolution of the empire in 1260, each of the successor states would be considered a super-power in modern terminology. Yet, the Mongols soon found themselves engaged in desultory civil wars rather than new conquests. How did it reach this point? Considering that the Mongols began their empire as a rather inconsequential power in the steppes of Mongolia, among a half dozen similar groups, another question comes to mind: Why were the Mongols successful in the first place?

Much of the Mongols’ success had to do with the appearance of Temüjin, the man who became Chinggis Khan. Before his appearance on the historical stage, the Mongols were but a minor tribe at a time when the Jin Empire (1125–1234) in northern China and Manchuria defeated an ascending Mon-gol khanate in the 1160s. Temüjin's father, Yesügei died in 1171, poisoned by Tatars, rivals of the Mongols. With the defeat of the Mongols, the Tatars dominated eastern Mongo lia. The Tatars were a powerful confederation bordering the Jin Empire, providing better access to trade and wealth. In the past, confederations like the Tatars rose to regional dominance and sometimes even held sway over all of the Mongolian steppes. Yet, the Tatars were not the only powerful tribe in the Mongolian steppes.

In Central Mongolia, the Kereit held sway. Ruled by Toghril Khan, the Kereit had close ties with the Mongols. Toghril had been anda or blood brother to Yesügei and became the suzerain of Temüjin. The Kereit, however, controlled the Orkhon Valley, which historically conveyed legitimacy to previous steppe empires.

While the Mongol military's role in their success is undeniable, both in terms of conquest and then retaining control, it was but one facet of the Mongol government, albeit the core to that institution. The Mongol civil administration also proved to be effective and innovative. This chapter will not be a detailed study of institutions and governmental structures—there are plenty of discussions to be found in the Further Reading section. Rather, we will discuss the philosophical underpinnings of Mongol rule and the implementation of those ideas. This philosophy and conception of rule was fundamental to Mongol success, at least in the short term.

The Altan Urugh (the Family of Chinggis Khan) at the Top of the Hierarchy

The government existed of several often-overlapping layers, each tied to the overriding conception of Mongol authority. The overlapping layers of authority both served to extend Mongol rule, while also placing limitations on individual power. The khaghan reigned at the top, but no matter who sat on the throne, the khaghan was never autocratic. The Mongol ruler had to weigh the interests of several factions. As Chinggis Khan had eliminated or diminished competing aristocracies, the altan urugh (Golden Kin) or the family of Chinggis Khan resided at the top of the hierarchy. As indicated in the previous chapter, the Mongols came to believe that the Möngke Köke Tengri had bequeathed the world to Chinggis Khan and his descendants. As such, it is not surprising that the altan urugh viewed the Mongol Empire as a sort of family business and they were the shareholders. While the idea of the Will of Heaven surely reinforced this view, it is clear that the preeminence of the altan urugh originated during Chinggis Khan's lifetime. He intended that his family (his descendants and those of his brothers) would be the aristocracy, replacing other lineages that existed in the steppes previously, as is shown when he assigned territories and people to his family.

Although it is not clear how large Chinggis Khan originally intended the appanages to be, after his death these patrimonies became better defined with most of the empire apportioned among the altan urugh.

The Venetian traveller Marco Polo wrote of the rise of the Mongols “[…] and when Chinggis Khan saw that he had so many people, he equipped them with bows and armor and went conquering through those other lands.” No one can discount the success of the Mongol military nor its importance in the creation of the Mongol Empire. It served not only as the instrument of conquest, but also the source of from which all other institutions originated. Yet, simply having a large number of men does not make a great army. Indeed, the term “horde” originates from the Mongolian word ordo. The latter refers to camp, but in English, it has become “horde”, meaning a large group of people with a derogatory connotation, such as being unruly. It can also mean “an army or tribe of nomadic warriors.” Nonetheless, even in this example “horde” still has implications of being ill-disciplined and barbaric. Furthermore, it provides a completely inaccurate depiction of the Mongol military.

While it is sometimes thought that the Mongols conquered with overwhelming numbers, this is an inaccurate perception. At the time of the 1206 quriltai, the Mongol army probably numbered less than a hundred thousand men and the population of Mongolia may have numbered one million. Even today, with modern healthcare, the population of Mongolia is barely above three million. Although Marco Polo unintentionally misleads us above, his next statement does bear some truth:

Marco Polo downplays the destructive nature of the Mongol armies (more on that later), and he is quite correct that the Mongols incorporated the defeated in to their armies. As mentioned previously, the defeated tribes of Mongolia were broken up and distributed into new regiments in order to form a single cohesive entity: the Yeke Monggol Ulus. Yet, not everyone became a Mongol. This privilege was restricted to the nomads.

The policies of the Mongols were as important as the actual institutions of their government as they dictated not only the Mongols’ actions and their view of the world, but also how others interacted with them as neighbours or subjects. What follows discusses the general policies of the Mongols. Exceptions can always be found but the following suffices to give a sense of how the Mongols operated.

The Will of Heaven

Militarily and diplomatically, the Mongols had a very narrow sense of the world. As they believed that Köke Möngke Tengri or the Blue Eternal Heaven had bequeathed the world to Chinggis Khan and his successors for them to rule it, therefore all peoples should submit before the Mongols. Failure to do so meant that they were in violation with the will of Heaven and thus a rebel. On this matter, there was no discussion. Various khans provided evidence to why this point was non-negotiable, such as the size of their empire and whom they defeated—if not for the will of Heaven, then how could this have been achieved? Thus while some observers found them arrogant, the Mongols also possessed a sense of awe for their accomplishments and expected others to accept what they viewed as self-evident truths. As a result, before the Mongols invaded a kingdom, they sent envoys who gave the ruler very simple terms which equated to “submit or die.” There was no third course of action. Attempts to negotiate terms did not go over well and may have been viewed as an effort to stall or as a passive form of resistance. Indeed, those who did resist would be destroyed, and usually the more determined the resistance, the greater the level of destruc-tion by the Mongols. Those who harmed the Mongols’ envoys could expect no mercy.

These policies contributed to the Mongols’ success in a number of ways. First, the ideology of Heaven's Decree assisted in providing legitimacy to Chinggisid rule and a counter to the claims of other authorities, such as China's own Heaven's Mandate, the authority of the Abbasid Caliph, and that of the Pope. The Mongols did not appeal to a higher power—that power had chosen them.

When Chinggis Khan (1162–1227) ascended the minbār at the Friday Mosque in Bukhāra in 1221 he announced, presumably through an interpreter, ‘O People, know that you have committed great sins, and that the great ones among you have committed these sins. If you ask me what proof I have for these words, I say it is because I am the punishment of God. If you had not committed great sins, God would not have sent a punishment like me upon you.’

It was a powerful and dramatic speech made by a terrifying figure at the pulpit. Chinggis Khan rationalises his invasion and destruction of the Khwārazmian Empire because he is the Scourge of God sent by God because of the populace's sins and the even greater sins of their leaders. To substantiate his claim, Chinggis Khan further explains through a syllogism that if not for their sins then why would God send a calamity such as the one that befell Bukhāra?

When reading this passage in Juwaynī, which later authors used as well, one must question whether or not Chinggis Khan actually uttered these words. For someone with limited contact with Islam, his explanation fits quite patently into Islamic thought, particularly regarding the legitimisation of authority and a fatalistic explanation of why bad things happen. Yet, did Chinggis Khan actually say or mean this? Or, rather, was it a simply a method by which medieval Muslims rationalised the violence that upturned Dār al-Islām? Certainly, other writers also wrote in similar veins, recognising that suddenly the Islamic world was threatened by a menace like no other. Other motifs were soon attached to the Mongol invasion, transforming the destruction from an expansive steppe empire into an apocalyptic nightmare, and Juwaynī was not alone in his penitential response to the Mongol invasion.

The origin of the Bukhāra speech is well known and merits but a brief explanation. Having absorbed the ruins of the Kara Khitai Empire (1131–1218) in 1218, the Mongol Empire now bordered the Khwārazmian Empire, another dynamic state in the early thirteenth century. Indeed, the Mongols arrival at the Syr Darya frontier of the Khwārazmian Empire had much to do with the expansion of the Khwārazmian Empire.