Where do you get your idea of the "standard view"? I've always heard the view that internal decline, late in the process, made Rome vulnerable to invaders it would easily have repulsed in the past. In fact, I have never heard anybody claim that random "barbarians" just waltzed up and posed any threat to Rome anywhere near its peak.

At least one explanation for the fact that the Fall of Rome is the only period of decline on the graph could be this: data becomes more scarce the further back in history you go. This has the effect of smoothing the historical graph as you extrapolate between the few datapoints you have. Thus the overall positive trend can more easily mask any short-term period of decay.

I fear you're beating up a strawman. As Gibbon makes pretty clear (and he's nothing if not the "standard narrative"), Rome rotted from the inside - politically and economically. The barbarians didn't get anywhere until Rome was practically collapsed from internal corruption.

Rome suffered an extreme case of all the standard things that modern economists write about - public choice failures, protectionism, price controls, government-backed trade monopolies, etc., etc. The political system was inherently unstable and tended to dictatorships.

The founders of the United States studied classical history closely, and consciously attempted to create a structure that would resist those failure modes. They succeeded better than they imagined (IMHO most of the American founders would have been shocked to hear the USA made it even 100 years, yet it's sort of still running today...sort of) but of course far from perfectly. They were aware that this is a hard problem never before solved in history (altho Switzerland has done pretty well too).

And, as you hint, lead pipes and lead poisonings didn't help any either. That was just bad luck.

Synthetic 'civilization' scores are unavoidably subjective

Just to be clear, the Ian Morris graph is Western Eurasia vs Eastern Eurasia(since it can't be Western Europe vs colloquial East, as Western Europe was a backwater pre-Rome)? I'm very skeptical of these historical score approaches, they obscure more than they enlighten and depending on how actual data is weighted the author can come up with any conclusion they want. 

For instance, why wouldn't population density be the defining characteristic of a successful society(higher energy density, more efficient use of space, all sorts of engineering style arguments favour that)? China would utterly dominate Western Eurasia in that model. I don't necessarily prefer that metric, I'm just pointing out synthesized metrics are very subjective though of course they have pop-history appeal.

Pet theory: Rome collapsed because all the greedy farmer soldiers became serfs

The fall of (Western) Rome has been the subject of 15 centuries of scholarship, so I'll just toss my personal favourite single cause to rule them all(it wasn't just one cause, it was multifactor but whatever): the collapse of the small-scale citizen farmers and the rise of the latifundia and the general demilitarization of roman citizens.

Disclaimer: the Romans were the historical villains of the region, in my opinion, I'm not glorifying them or their society.

The key contrast: Hannibal killed >100,000(?) roman soldiers while in Italy, yet never felt able to besiege the city. His army was maybe 100,000 strong. In 410 Alaric takes Rome with ~40,000 soldiers, despite the city being larger than the one that faced Hannibal, with no resistance worth mentioning. 

The problem is the composition of Roman society had changed. 

Growing Rome was a society where most fighting age males knew a bit of how to fight and could be drafted and would answer the draft out of patriotism/religious/civic devotion or greed. Late Rome was a society where a lot of people were coloni(proto-serfs) or fully slaves. They were purposefully not allowed to fight since their owners were afraid those skills might be turned against them. Late Roman society also wasn't expanding => the wars being fought wouldn't result in plunder => the incentive for citizens to join the army was greatly reduced. 

Early Roman soldiers had arguably unlimited upside, conquer some rich city or tribe and your share of the loot leaves you set for life. Late Roman soldiers just had a salary and much more competent enemies.

There were tons of rich land owners in the Italian peninsula, tons of people? How could the city fall to a mere 40,000 soldiers? No one really cared to defend it. The latifundiaries made their own deals with the 'barbarians', not caring about the fact that their families would slowly lose control of the land over the coming centuries. The religious(?) obsession with long-term legacy of the Republic and early empire were gone, the men of the Late west were short term focused. Early Rome elites cared about their prestige in Roman society, they saw themselves as part of the population of one city, at the end of the day they'd fight together against external societies. Late Roman elites had their wealth and power in the provinces and didn't see other latifundiaries as part of their in-group and worth fighting along with.

Plot twist: the latifundia grew because the farmer soldiers were too successful and wouldn't stop

The reason the latifundia grew and the old Roman system collapsed was the very success of the old Roman system flooding Italy with slaves and money and allowing elites to buy out small landholders. Furthermore a good reason for the Roman state to allow this process to happen was that the old get rich quick Roman war strategy ended up being used against Rome itself as Imperial pretenders persuaded our heroic yeomen farmer soldiers to turn arms against the state(since there wasn't much worth conquering outside the borders). Damned if you do damned if you don't.

Just for fun: modern democracies fuse roman legalese, revived roman civic religion, dying christian feudal ideas of obedience to authority and feudal cultural practices for peacefully transferring power

Epistemic status, wild fun speculation.

I'd argue that Western Europe continued evolving culturally and politically after Western Rome collapsed. The key technology that developed in Western Europe was the (comparatively) peaceful transfer of power from one monarch to another upon death, without lobotomizing the monarch and replacing him with a weaselly bureaucracy the way the Ottomans/Chinese harem systems solved the endless succession civil war problem. 

The ability to ACTUALLY transfer power, as opposed to sidestepping the succession by having real power embodied in a constantly regenerating collection of people is the enabling cultural technology for modern republican democracies. Better put: both elite and popular culture expects a peaceful, legally codified transfer of power. It's this ingrained instinct that's valuable and is essential(and can be lost, as Republican Rome lost it and Imperial Rome never acquired it in the West), rather than the formal rules for how you transfer power. 

That and Europe's weird obsession with separating the person of the king from the institution of the monarch(see Britain's linguistic weirdness around King/Queen-in-parliament, possibly related to Christian weirdness around the Trinity, maybe the religious mental calisthenics got applied to political ideas as well) creates a neat interface where you can cleanly replace a monarchy with an elected government and it sort of all just works the same in the minds of everyone involved.

One thing to note here is the automatic assumption that Rome was "greater" than Medieval Europe. This is anecdotal, but if you look at technological progress from 200BCE (the Punic Wars) and 200AD, you find that not much has happened, except the expansion of trade networks.

Meanwhile, the 400 years from 476CE to 876CE saw the growth of the Frankish Empire, the subsequent Holy Roman Empire, the invention of the heavy plow (note that Rome had been in control of Gaul for 520 years, and never invented it) and further discoveries by Catholic monks. In fact, analysis on skeletons show that people were better fed after the fall, not before (I'll see if I can dig up the citations for these).

Rome did succeed Europe in some ways (namely architecture, central planning, and infrastructure), but it wasn't more "advanced" per se. All of the buildings, roads, and aqueducts still stood after Rome fell.

Your main point --- how Europe was able to stand up to outside pressure while Rome couldn't --- still stands, but we shouldn't consider that it was "better" in some way.

Welcome to the study of the rise and fall of states, empires, dynasties, civilizations. Also see: Toynbee, Spengler, undoubtedly many other historians east and west. John Glubb's "Fate of Empires" even argues for a specific life expectancy of empires, 250 years. 

The social development graph is unclear to me. How does Ian Morris define "east" and "west"? Is Egypt and the Levant "West" or "East"? We don't usually consider Egypt to be part of "the West" these days. From the perspective of Ancient Rome the Levant were as farther east as Asia [Roman province] but if you look at a globe they are both on the western side of Eurasia. Whether Cairo and Constantinople constitute "east" or "west" gives the graph completely different meanings. Does "East" include Arabia and Persia? How about the Levant? My guess is "West" refers to Europe and the Mediterranean and "East" refers to India and the Sinosphere.

I think this analysis could benefit from a broader perspective. The knowledge of Rome wasn't lost. The Renaissance didn't happen in a vacuum. The European classics were preserved by Arabic scholars [LW · GW] during the European Medieval period. The Byzantines survived until 1453. They were the legitimate Roman Empire.

Western historians traditionally view the collapse of the Western Roman Empire as a deviation from normalcy. I think about the rise of the Western Roman Empire as the anomaly and its collapse as a return to normalcy. Rome's grain came from Cairo. Egypt was the center of Mediterranean civilization for the first half of history. It makes more sense that Egypt, not Italy, be the locus of Mediterranean civilization.

If you're curious to learn more, a terrific resource is The History of Rome podcast by Mike Duncan which walks you step-by-step through the rise and fall of the Western Roman Empire. From listening to that podcast, I think the destabilization of Rome started with an influx of slaves which increased inequality and drove citizens out of work. Internal economics broke democracy which brought about Caesar's autocracy. Mike Duncan isn't surprised because the Western Roman Empire fell too early. He is surprised it survived Crisis of the Third Century.

What if it's just regression to the mean? Maybe the main problem wasn't that late Rome was unusally bad, but that Rome at it's peak was anomalously successful, and this didn't last because technology and culture just wasn't able to sustain an anomaly at the time?

-