The collapse of a late empire is instructive. A late empire can be described as one which is at the pinnacle of particular technological relationships. Often such a late empire rises quickly under a few leaders, and then collapses just as quickly. Two paradigmatic late empires are Alexander's late antiquity empire, and the late medieval empire of the Mongols.

Each one rested on a particular imbalance, where a highly mobile and powerful military force was able to rapidly overwhelm a series of older states which had inferior mobility and firepower, and a greater share of their resources locked up in administration and control. Both empires broke up rapidly after the founder, and both spread new culture and ideas widely. Their burning glory pales beside the dissemination.

Late empires are not always associated with energy shifts, but in the case of the Mongol Empire, it is. The Mongol empire was the most powerful empire that could be built on the wave of technology that comes from the dawn of the age of metals, agriculture, and domestication of large animals. It was born in 1206, and by slightly after 1400 all but one of its important successor states was gone.

We have seen three major transitions of energy basis in recent times. From muscle to water/wind, which was the baseis of the mechanical economy. The second was from the mechanical economy to the coal/steam driven economy, which was the basis of the industrial economy. The the third was to the petroleum driven economy, which is the mechanized economy.

To compare this, there had been only four significant energy revolutions previously in the history of human kind: domestication of large animals, the agricultural revolution, the early wind/water economy, and the application of draft animals to war and plowing in the medieval period. That these do not have clear names shows how little the inter-relationship of energy and history is studied. We can however say that the first major revolution comes with the beginning of the metal age and the end of the stone age as the harnessing of fire for metallurgy, the harnessing of land for crops and the harnessing of animals. While cities flow out of this revolution, the other group that is created by it are migrant herdsman, who use its technologies in animal handling.

These two forms of this economy exist at the knife edge. Cities have better technology, more population, writing, trade. They are also shorter because they don't eat as well, and they don't have the military and hardship ethos that drives "barbarian invasions". It is important to realize here that a "barbarian invasion" is not an invasion of neo-lithic, or even micro-metalurgical peoples - people who have access to iron of a high purity, often a meteorite - but peoples who are as developed, in their own way, as the city dwellers. We will see this dynamic: static civic economy against mobile tribal economy played out over the course of four thousand years, as progressive centers of civilization are invaded and overthrown by horse mounted herding cultures. The last can be said to be the Yuan Dynasty of China, though a case can be made for the Europeans having used much of the same dynamic in the conquest of the Americas.

We can term this the horse/house conflict, where the highly mobile versions of a technological era fight with the highly developed and civic versions.

The last stand of this conflict was found in the American West, and in the areas of Central Asia. Wounded Knee being the last battle which was actually in doubt. But even today, civilized and advanced cultures face difficulties in Afghanistan. The horse/house conflict, while it is over, was the single longest running conflict in human history, and it is with us in outlines even today. It's final resolution is only a bit over a century ago. There are people alive today who knew people during that time. They are old, few and dwindling, but they are there.

The second revolution comes in as the invention seafaring brings larger empires and cities, or the political economy. Long distance trade, allowed by better riding and ships creates the pressure for writing, as well as the need to plant at the right times creates the need for astrological time keeping. This economy as well has horse/house versions, however, the civic house version has started to gain the upper hand, but not so much so that the same problem comes to the front. House economies depend on agricultural heartlands, and must upkeep cities. Horse economies do not have to expend energy in dealing with the city problem or the heartland problem, they are larger, well feed and aggressive. The new antiquity economy was able to hold off invaders, often by building long walls, in Europe and China and other places, and by turning seas within its reach into private ponds.

Then end of antiquity can honestly be said to be the point where virtually simultaneously a series of horse mounted cultures overwhelmed the empires of the day. Work on the transition form antiquity, I am told, is not a glamor area, but for our purposes of studying energy, there is an important point. The house economy of that time had to expend enormous energy in controlling water, distributing food, and administration of the complex of the economy. There was a great deal of "wealth", but more and more of that wealth was locked up in maintaining, not improving, the status quo.

When I was an undergraduate, there were discoveries about how late antiquity made enormous advances in a number of areas, only to be swamped by invasion. This evidence has
only grown higher.

The last pre-modern transition comes with a few relatively unheralded inventions that radically change the muscle economy. These are, the are the lateen rigged sail, the horse yoke and the stirrup. These allow greater extraction of the first wave of the human economy: more acreage, more speed, better sailing times, more impact from horse warfare. While developed in the 600-1000 period, they remained in service until the opening of the 20th century, the reason being that a later wave of innovations on these ideas would produce the first modern industrial revolution, and the attachment of coal to a heavy and cumbersome fuel would mean that in large parts of the world, out of the reach of rail and large ship, they would be economical and easily built without large concentrations of capital.

The modern transitions begin with the last wave of this wind/water economy. They are conceptual revolutions. While coal is given the glamor position, or perhaps gunpowder as a combustion fore-runner of it, the reality is that much of the improvement in living standards and wages comes from globalization.

To explain. Through out the middle ages, there was relatively limited contact between the various global centers of civilization. India and the Middle East were in close contact, China somewhat more distant, with Europe and Japan being more disconnected still, and the civilizations of the Americas being in only irregular contact, and the sea faring cultures of the pacific having a very loose joining to much of the rest of the world.

However, with the closing of the medieval pressures, the increase in trade speed of the wide adoption of algebraic based navigation and the lateen sale, Europe, the Islamic World, India, and China had a dramatic burst of increased trade in ideas, goods, and political power. This trade had been continuous, as the history of major world religions shows, but during this revolution, a series of pieces that had been, in aggregate, separate, fell together through invention, discovery, conquest and political organization.

The period from 1400-1800 is driven, not by coal or steam, but through the advancement of metalurgy, mathematics, the acquisition of crops and wealth from the new world, and most importantly, the integration of global knowledge.

Many of the individual inventions were present for centuries: gunpowder, the printing press, the astrolab, zero - one can make an extensive list of the parts. However the question of what created the assembly must fall to a series of changes, not the least of which is was the creation of one of the last great horse empires: the Mongol Empire of Genghis Khan. This created a single land ocean - horse driven - which allowed ideas and goods to flow. They were in small quantities, slow, and expensive. But the crack was there. Equally important was the massive disruption caused by the bubonic plague outbreak known to history as "The Black Death".

In essence, the Mongol Empire was the best empire the muscle driven economy could produce. It's collapse, like the collapse of Alexander's empire, left behind a host of states which had the pieces of a new world, and the cross fertilization allowed more of them to be put together. As many have pointed out, it was not clear what, exactly lead to Europe being the heartland of a series of world spanning empires. Geography, culture, and other forces are all part of the mix of explanations.

The collapse of this empire is a typical pattern, what can be called a "late empire" which is the best version of the old economy. It is driven precisely by the end of the s curves of that economy: it is harder and harder to get pure advantage, and the path of least resistance is to put all of the resources under a super-power which does little but govern. This centralization allows an enormous burst of innovation and dissemination, even as it also promotes localism of those features which do not concern the main empire. Large empires of this kind are often excessive, brutal, and run by individuals who have a clear and direct focus on the empire itself. They also tend to collapse quickly precisely because the neither have many new innovations, but at the same time they usher in innovations. Their very existence undercuts the rational for that existence, and the superiority in mobility that their existence relies upon.

The Mongol empire, and its major successors, including the Yuan dynasty of China, were at the cusp of the transition from the muscle economy to the mechanical economy. What they lacked, navigation, higher density crops, better ways to harness water power, the calculus and macroëconomic theory, is important to understanding their collapse.

The folk explanation for Europe's rise is that it was more entrepreneurial. This does not stand up to scrutiny. In almost every category of commercial theory and economic practice, China was ahead of Europe at that time. Law, paper money, corporations, regular mail sytems, and banking, to name just a few, were all more advanced in China. Chinese entrepreneurial culture was more, not less entrenched, China had factories before the west. As research has been highlighting for over fifty years now, Yuan and Ming China, not Renaissance Europe, lead the world in economic development, had a far larger GDP, even with Purchasing Power Parity thrown in, and the long practice of establishing centers of excellence around production. China's volume of trade was far higher in proportion to its GDP, it had unified customs and a central market.

In short, if the competition between China and the West were based on laissez-faire economics, Shakespeare would have written in Chinese, because it was not even a contest.

But we know things didn't work out that way. The seeds of why can be seen in the rise and fall of the Mongols.

The Mongol Empire is conventionally dated from the great assmebly of 1206, where the man who would become known to the west as Genghis Kahn took control of the Mongols, created new laws, and launched a career of conquest which would last until his death in 1229. His successors Ogedei and Mongke while not gaining the notoriety to history would conquer many of the most economically valuable areas, including much of China, and created the ability of the Mongol empire to be a land ocean, where trade on the Silk road could flow.

The weakness in Mongol control, both in its own empire and in the Yuan dynasty, can be found in several advanced features which were hobbled by lack of a theory to organize them. Two of the most important are the assembly or Khuriltai and the other was the creation of a large economy, which would eventually include a postal system and paper money system.

Both of these would bring the Mongols to grief. The first because at critical junctures the commanders and princes would have to return to the assembly to elect a new Khan on the death of the old one. The second because while the Mongol empires had unified trade, communication, and eventually banks and fiat money, they lacked the understanding of money quality and quantity to prevent inflation. The Mongol Empire, and the Yuan Dynasty, both collapsed because of internal economic division, and political disunity.

The core point here is that once a late empire reaches its full size, it has two pressures. The first is that the guns turn inward, and struggle for control of the empire washes away all other concerns. The second is that they are incapable of pricing their own system of conquest. Conquest is enormously expensive. The Mongols slaughter millions of people in their wars, and since they had no industrial base of their own, had to pay for this with conquest and plunder, or taxes. When there were no profitable areas to conquer, the empires were living on borrowed time.

Thus despite a very entrepreneurial base in China, advanced law and commerce, the late empire of the Mongols collapsed as rapidly as it rose.

The replacement empires to the Mongol and Yuan dynasties were very different.

The first important difference is that by 1405 when the last central Asian state, the empire of Tamerlane, the era of land ocean empires came to an end. It was a period of less than two centuries, and even though it had established the largest contiguous empire the world has yet seen, it rested on the ruthless exploitation of people who essentially lived on horse back. They conquered, but could not enjoy the fruits of the conquest.

This is a typical pattern in the horse/house conflict. The nomads come, the nomads conquer, the nomads get used to pillows and concubines.

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The Mongol military machine rested on three cores. The first was the horse and bow core of the nomadic empire. Longer range bows fired from horse back. The second core was the absorbing of the turkic peoples, and the creation of a high level of standardization and discipline. The third was the absorbing of Chinese mechanical innovations, including gunpowder and siege craft. Early Mongol efforts at conquest were rapid over their central area, but were limited to attack and demand tribute over other areas, including Jin China. However, the acceptance of the Turkic peoples into the empire, with their relationship to writing and administration helped provide the sinews of being able to wage a long war against the Jin. The Jin, in turn, would be the source of siege machines. A fast army able to defeat other arms, and maintain coördination in multi-pronged attacks, which could then assemble siege machines and destroy cities, was the crucial combination.

However powerful this combination ones, it is also extremely expensive to maintain. Both in calories and in social cohesion. A world filled with fast mobile commanders governed by personal consensus works only so long as the size of the empire permits personal contact. Personal fights marked each later succession, and the empire convulsed repeatedly. Without transition of power, every move became about position for that transition. When the rewards for taking the central prize outweighed those for conquering, the empire turned inward. This pattern is well noted to historians. However, frequently they do not notice the relationship of technology and society.

What comes next is the story proper of the emergence of what is the true first of the industrial revolutions, one based on iron, navigation, wind power, combustion, water power, high density crops, mathematics, and printing. The Mongol Empire made several innovations, and adopted others, as importantly, it created a short period where there was massive dissemination of knowledge, which continued even after the collapse of the empire.

It is far too simplistic to attribute what follows to the Pax Mongolica, but it is part of what would place a series of states in position to pursue a new energy basis economy.