So before getting into the meat of the question, let's start with the appetizer - the salad. The caesar salad was not veni'd, vidi'd, or vichi'd by Julius... but is instead attributed to Caesar Cardini in the mid-1920's. ;)

OK, so, yes there were positive aspects to the Mongol conquests - at least taken from a certain point of view (and, as with the creation of the autobahn, you have to block out a lot of negative effects in the process.)

That said, let's take a look...

#Pax Mongolica

Like its namesake, the Pax Romana, the territories already living in submission to the khans "enjoyed" (if one can use the term) living conditions that were remarkably stable, lawful, and free of crime and violence. This prompted historians like Juvaini to comment,

For fear of his yasa and punishment his followers were so well disciplined that during his reign no traveller, so long as he was near his army, had need of guard or patrol on any stretch of road ; and, as is said by way of hyperbole, a woman with a golden vessel on her head might walk alone without fear or dread.

Though he says outright it's hyperbole, it does effectively convey the idea that life before and after the Mongol rule of most of central Asia was often, as Hobbes would put it, "nasty, brutish, and short." On the other hand, though the yasa system of laws was exceedingly strict, living within the empire would have been far easier and more predictable that the factional infighting of nomad confederations many of the people had lived and died under.

Along similar lines, the enforcement of the yasa across Asia allowed trade routes that had long been abandoned as being too dangerous, to once again open and flow with merchants and goods. The most famous of these, of course, is the Silk Road network, which had been virtually abandoned to bandits and raiders following the collapse of the Chinese Tang Dynasty's control over the Xiyu western protectorates in the mid-8th century. The communications system of the Mongol Khannate was also a model of 13th century efficiency: the system, called the Yam, consisted of relay stations maintained at regular intervals across the empire, where riders and horses could send messages - in a pinch - as far as 4-500 miles in a single day, and across the whole of the empire - from Karakorum to the front lines in Syria, for instance - in as little as a couple of weeks. Though initially the Yam was extensively used by many officials within the Imperial bureaucracy, following the kurultai in 1251 Möngke Khaghan restricted its use. From Allsen:

Princes, officials, religious dignitaries, and ortogh merchants had become accustomed to using the jam for their personal needs, thus clogging the empire's lines of communication and adding to the already heavy burden on those households of the populace assigned to maintain the relay stations. Henceforth only officially authorized personnel would be allowed access to this system.

#Religious Toleration

Markedly unlike many other empires of the world in the 13th century, the Mongol khans were not particularly interested in strictly enforcing any single, overriding faith on the populations under their control. Though the early Khagans like Genghis and Ögedei were practitioners of the native steppe religion known as Tengri, later khans adopted several alternative faiths. Möngke, the fourth Great Khan, extensively favored Nestorian Christianity, and even dallied with the idea of actual conversion - though he never carried that out. Berke, the founder of the Golden Horde, for instance, was famously the first Mongol khan to become a Muslim. Heck both Genghis and Kublai actively sought out and invited Christian missionaries from Europe in order to better understand their unfamiliar faith, and Genghis rather famously sought out Taoist priests to inquire about the possibility of immortality.

Nonetheless, in virtually all cases, regardless of which religion the khans themselves favored, they never coerced their people into conversion, and ruled over a broadly multispiritual state that was very much out of the norm at the time. The European Christians and the Islamic caliphate were at this time locked in holy war against one another... even the Chinese empire was only a few centuries past its final great anti-Buddhist purge in the 9th century. Yet under the khans, there would be no purges for religion's sake. Even the thoroughly Muslim Timur/Tamerlane in his conquests of the Indian kingdoms implemented a stable system of Muslim administrators ruling over a Hindu population.

#Cultural Melting Pot

The poeples of the steppe that had coalesced under Genghis Khan into the Mongol Empire had never been a single culture. Just the initial confederation consisted of more thana dozen tribes... here, for instance is when the sons of three tribes initially proclaimed Temujin as their Great Khan, from The Secret History of the Mongols:

When Altan, Qučar, and Sača Beki took counsel with one another together and spake unto Temüjin [saying,] “We shall make thee to become khan. If [thou] Temüjin become khan, we, hasting as spies unto the many enemies, maidens and ladies good of beauty, palace tents, ladies and maiden comely of cheek of realms and peoples, and geldlings good of rump, making [them] to trot, we shall bring for [thee.]

If we hunt crafty wild beasts, we shall go out beforehand to compass [them] for thee. We shall press [them] for [thee] in such wise that the bellies of the wild beasts of the steppe become united together. We shell press [them] for [thee] in such wise that the thighs of the wild beasts of the cliff become united together. [...]

Thus pledging [their] word, thus swearing an oath, they made Temüjin to become khan, naming [him] Genghis Khaghan.

Over the course of Genghis' reign, and those of his successors, the standard Mongol policy was to take anyone of use or skill and relocated them wherever they were needed. While this would have been undeniably highly traumatic for those "selected," one can say that such cultural diffusion (forcible though it often was) resulted in transmission of a great many ideas, technologies, and cultural touchstones that may have otherwise remained segregated for far longer. Written language, for instance was adopted by the Mongols when Genghis became aware of its utility. The Mongol, without a written script of their own, simply adopted the script of the Uighur tribes within their confederation. As the Empire spread, so too did knowledge of reading and writing among the until-now illiterate nomad peoples of the steppes. Political and technological innovations from the Northern Chinese were likewise diffused across the empire when it became clear that - once again, in words attributed to Genghis - "the empire could be conquered on horseback, but could not be governed on it." As the Empire fought against the Jin and Xi Xia Dynasties of the North, and then the titanic struggle against the Song in the South, Chinese weapons tech like siege engines, rocket artillery, and gunpowder-based weaponry was captured, studied, and replicated by the Mongols (or more accurately, by Chinese thralls of the Mongol overlords), and then "transmitted" Westward to the frontlines of the Islamic Calophates and Eastern Europe, where cities like Baghdad, Kiev, and Vladimir all learned firsthand of their terrible efficacy. Likewise, the Mongol invasions of Eastern Europe also saw the initial formation of the Russian identity, as the independent Kievan Rus city-states were forced to band together in an (ultimately futile) effort to resist conquest.

#But... This absolutely should not be taken as some kind of apologist position on my part for the Mongol conquests. It must never be forgotten that the "positive features" of the Mongol Empire were vastly overshadowed by the unbelievably immense human cost - 40-100 million people systematically slaughtered, the destruction of Baghdad, and both Northern and Southern China - all three some of the world's most complete repositories of ancient knowledge - simply put to the torch. With the "positive" of the Silk Road and cultural/technological transmission came the open of those same route to transmission of another kind: pathogenic. It's widely understood that the Mongol union of Asia either caused or at least greatly exacerbated the effects and reach of the infamous Black Death, which would go on to claim another 75-200 million lives across Eurasia in the 14th century.

Though we can (and I just have) sat here and said "yes, some good things did come out of the Mongol Empire," that does not change the fact that such (relatively minor) benefits came from the brutal destruction and/or subjugation of the majority of the world's population... and that such an event is correctly seen as one of the great tragedies of all time, right up there with and alongside the likes of the Holocaust, the Great Dying of the Americas, the Transatlantic Slave Trade, the Great Leap Forward, and the Cambodian Killing Fields.

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#Sources Allsen, Thomas. "The rise of the Mongolian empire and Mongolian rule in north China" in The Cambridge History of China, vol. 6: Alien Regimes and Border States (ed. Herbert Franke and Denis Twitchett).

Cleaves, Francis Woodman (tr.). The Secret History of the Mongols. [PDF]

Juvaini, A. A. The History of the World Conqueror. (Tr. Boyle, J. A.)

Weatherford, Jack. Genghis Khan and the Making of the Modern World.

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