Future Empires are going to be very different, the loss of ethics, effectiveness plus changes to the maritime environment will ensure this
No matter what else you say about the American empire and the global system, there is one very important fact that is often ignored in the overshoot sphere
I'll show it in graphs
And another important graph
The first graph speaks for itself, wars are basically disappearing, unfortunately I can't find a graph which goes back earlier. However in per capita terms across all of history WW2 is the 6th deadliest war (numbers 1-5 are all pre-enlightenment) while WW1 isn't even in the top 10 so this trend has some history. And the wars we do have, like Afghanistan and Iraq, are better thought as mass policing actions than conventional wars, notice the lack of clashing armies and mass bombings. The second graph however requires a bit more analysis to truly understand the significance of the figures, it's death's per million and it is decreasing over time. While the major atrocities aren't as common anymore whole the ones that don't happen have less of an impact. Also, note that the graph above is for political violence, so the net cast includes a lot more than wars.
Today, the world's population is around 7 billion and outside of periodic spikes the annual death toll total is between 30,000 to 45,000. Or in percentage terms from 0.0004% to 0.0006% of the population per year (the largest spike killed 0.006% of the worlds population), in comparison the percentage death tolls in tribal societies is about 1% of the population dying to war every year (if that was the case now, 70,000,000 people would die from conflict alone every year, i.e. more than in all of WWII). But lets look at the death tolls from 3 sequential battles from the second Punic war that occurred in separate years. The battle of Trebia (218 BC), total death toll 30,000-37,000, the battle of Lake Trasimene (218 BC), total death toll 17,500 and lastly the battle of Cannae (216 BC), total death toll 64,200-85,700.
The lower estimates add up to 111,700 dead in 3 years, or 37,233 dead a year, which is about the current annual death toll. But that was only one campaign in the second Punic war, Rome invaded Spain to cut off Hannibal's supplies while he was in Italy (their good legions were elsewhere) and invaded Macedon when the latter sided with Carthage, burning Corinth to the ground. And there were other wars going on around the world, while the above only includes soldiers who died in battle, the civilians who died as Hannibal scoured the Italian countryside aren't included.
And the world's population was tiny back then, so as a percentage the death toll would be far higher than it is today. And if I wanted to I could look at the likely death tolls of North and South America before European contact, when the Amazon jungle didn't exist and instead the area was covered in city states (who historically fight a lot) while up to 100 million people could have been living in North America. The death tolls from the Americas could have easily been a 1 million or so a year by conflict under certain assumptions.
So, I hope that single important fact about the global system and the US empire is clear. Whatever else, they are incredibly effective as forces of peace in the world, holds high ethical standards and commits barely any atrocities by comparison to older empires.
Translation; the American empire is the hippie of empires.
Also as a side note, the people who talk about war getting easier and therefore more common don't have a clue. The statistical evidence, and this reaches back to the tribal wars of pre-civilization (admittedly through modern counterparts), is that as war becomes more deadly and easier to fight, we fight less and casualties decrease. This effect actually makes sense in game theory and psychology, we have a set level of risk (consequence x likely hood) we like to accept. Interestingly this effect is even more pronounced with drone warfare, along with decreased civilian casualties, 70-90% of drone kills are terrorist which compares nicely to WW2 in which only 33% of deaths were actual combatants. So yes drones kill innocent civilians, but does every other form of warfare, drones just kill less.
In comparison we have the British empires actions 60 years ago in the Mau Mau uprising. Here's the war nerd talking about that, Monty Python Burning Kikuyu Skit. Here's the book, Imperial Reckoning, which talks about the British response to the Mau Mau killing 32 white settlers. That response was to intern 1.5 million people in concentration camps, the entire Kikuyu ethnic group, and kill about 300,000, or 1 in 5, of them. This was also how the British dealt with the Boers, killing 25% of the civilian population via concentration camps. We could also look at the Japanese attempt at empire, WW2, where they killed at least 3 million Chinese with the Three Alls Policy (kill all, loot all, destroy all) and overall could easily have killed 10 or so million civilians. Julius Caesar bragged about killing 1,000,000 Gauls and enslaving so many (about 2,000,000) that he crashed the slave market and the Assyrians did much the same, "I flayed many withing my land and spread their skin out on the walls" (Ashurnasirpal), but in very inventive ways such as burying people alive in a pile of severed heads.
In regards to the behaviour of the US empire in regards to its atrocities, it is in no way comparable to other empires. This isn't to say that the US empire is a force of good or nice, merely far less violent and sociopathic than most empires. It, along with the global economic system, is also incredibly effective at enforcing peace and doesn't get into any of the traditional large scale wars.
It is highly unlikely that future empires will behave like this. Future empires will be brutal and not via proxies, but directly. They will also not be nearly as effective in keeping the peace and will fight far more wars because of that fact. Going into entire regions and killing thousands to millions of people isn't uncommon behaviour for empires. One, these wars will be far more closely linked to survival than the ones we currently fight (Afghanistan and Iraq aren't existential threats) so more drastic measures will make far more sense to those involved (due to the fact wars will now happen closer to home and there will again be less technological disparity). And the disruption caused by climate change and economic shocks isn't going to make areas easy to control, in addition to decreasing the resources available, and a knee jerk reaction to that is just to enact atrocities and mass killings (both works and doesn't work, but that's another discussion). Armies are likely to reverse the process of becoming professional, due to the decreasing prosperity of the world, which will increase the incentives for soldiers to commit atrocities or torture locals (like slowly roasting them, common in the 30 years war) since that's how they get loot (bonuses) and it's an easy way to gain supplies. Of course there is going to be a change of ethics and values caused by the decline, quite a lot of the old values will reappear, the ones that are fine with raiding, mass killing, the sacking of cities and such events. After all, one solution to the Food vs Fuel debate is for wars to be the decider for which countries starve. That attitudes certainly not new, the Roman republic bought a temporary end to taxation with its conquests, fuel and food is just another form of wealth, as the shipments of Egyptian grain to Rome proved.
Also on the changes likely to hit insurgency and counter-insurgency, I think a short story will do. In the American civil war Sherman encountered the first IEDs, buried artillery shells with a trigger mechanism, he managed to stop the confederates burying anymore shells by marching confederate prisoners in the front of his army.
Another change relates to how easy sea denial will become. This article talks about that in relation to the Asia-Pacific. A navy has 2 main jobs, to deny the enemy the use of the sea (sea denial) for transport while enabling the transport of goods and troops across the sea (sea control). Before WWI if you achieved one the other was automatically achieved as well, but then subs came along. Suddenly it became extremely difficult to stop the enemy attacking friendly shipping and so sea denial and sea control became 2 separate objectives. With the advent of drones, missiles and better sensors, this division has only widened.
The age of maritime empires is ending, the days when Britain ruled the seas is over and no one can replace them. China could have its access to the sea cut off by Japan, India, Indonesia or any other power with the necessary technical know how. Their access to the world's markets, like Africa or South America isn't very militarily secure. The sheer dominance that Britain and America experienced won't exist again. Of course there are ways to mitigate this problem, but the central fact that dominance of the sea is becoming unobtainable will stay. Put it like this, the tricks the Chinese use in JMG's story "How it could happen" could just as easily be used against the Chinese, but against their civilian shipping (the traditional targets of subs after all) instead of military ships. And importantly, it doesn't take a great power to pull the trick off. Which is probably largely why countries with sufficient know-how don't fight each other, since we like having the global trade system working smoothly. The best case scenario is that China is simply constrained in what actions it can take but no one actually has to use their threats and fight some wars.
The original use of aircraft was for reconnaissance, drones (which are Vietnam war old) are cheap and could easily fulfil that role across large areas. Missiles are incredibly precise weapons, if you see a target you can hit it, though how this is achieved will likely change with peak oil. And any defence that is put onto civilian ships reduces cargo space and significantly increases cost. Now the limited date we have on ship board anti-missile defences (an Israeli-Egypt and a Russian-Georgian skirmish) indicates that modern navies can survive missile barrages if they are prepared, and being in the missiles extreme range helps, but that doesn't help civilian ships and honestly, the data is too limited to say, ultimately we don't know how contemporary naval warfare works. And sea denial is all about denying the enemy access to the seas transport routes, for economic or military purposes, or hitting civilian ships. The opponents navy can be completely ignored, as long as you can practise sea denial.
So we will likely see a return to land based empires, like Rome or Persia. The Aztec's didn't really have much in the way of ships and the Mayan city state empires acted without them as well. This means empires will be more localised (continental rather than global) and land based infrastructure will matter more. As it stands, this is a return to the more standard form of empire and the end of maritime power as a hugely decisive influence on the world.
Globalisation works a lot better than most people admit, also actual aristocrats damage economies along with traditional totalitarianism
This article has an observation that is is fairly important to understand globalisation, specifically section #5. The weakening of the middle class/economic troubles in America, Europe and here (the auto industry) is largely caused by and part of about 2,500,000,000 people being lifted out of poverty. Also the creation of a large middle class in China.
Globalisation, importantly, works on a global scale. The inequality inside the first world is virtually nothing compared to the inequality between the first and third world (in the first world, clean water, safe food and basic necessities are almost guaranteed ). " It's just that we're all that rich man". And the majority of first world governments offer a safety net so that the poverty of the first world is not equivalent to the poverty of the third world. For peasants in Asia the appropriate phrase for hundreds (if not thousands) of years was "[They're] so deep in water that a single ripple will drown them".
Globalisation is actually working to reduce poverty and global (not local) inequality. It just can't do that without redistribution. After all, when manufacturing jobs leave for overseas, they don't disappear. importantly, sweatshop labour is actually a better deal for people in the third world than most other options (also a way out of poverty), see this. And it may not be working all that well, but it is the only thing working on this scale.
There is a list (in German) of all the different reasons given for why Rome fell, it numbers 210 different explanations. Some of them are silly, others stupid, but quite a few are perfectly plausible. The causes of complex events and trends are never very clear and the effects of overshoot are exactly like that. There will always be other explanations that could be the cause of trends that overshoot causes and vice versa. The world is not nearly clear cut enough to be otherwise. As above, globalisation provides an alternate explanation for job losses compared to overshoot, along with the decline of first world countries relative to third. And the growing richness of the third world is also a alternate explanation for oil price volatility, decreasing supply doesn't need to be brought up. These other explanations may not be nearly as good, some will be silly or stupid, but they will exist and most of them will have some existence and impact. One of the hardest parts about guessing the future is the fact that something vital will be missed, maybe it will only change a minor detail (whether city x survives or dies), something bigger but not big picture changing (area x preserves modern technology during dark age) or it could be a big picture difference (steady state vs decline).
Another thing that is important is that we currently lack almost all the totalitarian instincts of previous societies. Here I'll be using the definition of a society that attempts to control all spheres of life.
Heretics, religious and intellectual, used to be burnt at the stake. While this practise was more a medieval christian one, the ancient pagans also practised it as evidenced by Socrates's trial,
"Socrates is guilty of
crime in refusing to recognise the gods acknowledged by the state, and
importing strange divinities of his own; he is further guilty of
corrupting the young.". For those crimes he drank hemlock and importantly that sentence was carried out by a democracy (newly established) so it was a totalitarian instinct carried by the people, not just the rulers. We may isolate or ignore intellectual heretics, but we don't exile, torture and/or kill them in various public spectacles (mind you, due to the martyr effect the former is more effective at preventing their ideology spreading, which has its own consequences).
But we don't do that anymore and freedom of religion is guaranteed in most of the first world. We don't carry out devastating religious wars, crusades or purges that kill millions of people and devastate large areas. The religious totalitarian impulses also spread into intellectualism, one specific is that curiosity is a sin. The difference isn't that these impulses don't exist anymore, here's a recent article talking about condemning curiosity (note the professor of divinity and his book) and most people think the message of Frankenstein is Science is Bad, even through the actual moral/message is different, what happened is we started being tolerant (because religious wars suck) and forcing arguments to not resort to violence as a first step, valuing order and peace. Also we went and became modern in moral and ethical issues, Chesterton and C.S Lewis are primarily modern in their stances and just happen to be Christian as well.
How Asia Works attempts to explain why different Asian countries look so different (specifically the rich North-East vs the poor South-East), South Korea is a rich modern nation, while the Philippines is poor even through it was originally far richer. The very first step that all the successful countries (Japan, Taiwan and South Korea) did was to redistribute land, placing small caps on maximum land ownership were common, to as many people as possible, note most people who farmed before this didn't own land but merely rented it (often feudal relations). The first thing this did was to rapidly increase production per hectare (but importantly not profit per hectare or production per labour unit) which had various knock on effects, such as capital generation and a better trade balance. He mentions that when Latin America was building up its industry, the middle class grew because of industrialisation, hence Latin America started consuming more meat and because Latin America's agriculture hadn't gone through sufficient improvement, this caused all the wealth generated by industrialisation to be spent on importing meat and higher quality foodstuffs.
An interesting observation is that an (almost) perfect free market was created in Japan for agriculture. There was a huge amount of producers with equal access to capital, the government provided a broad range of support (like loans for irrigation) that included marketing and information (an assumption in perfect markets is access to perfect information). This (almost) perfect free market worked as well as theory said it would, creating lots of wealth and improving the public good. But more importantly, breaking up the traditional power structures worked, and this is especially true for traditional aristocracies along with feudal structures that are similar to ones police states possess.
Related to the above, I've been doing some basic research on various NGO's that attempt to help the third world. One observation, capitalism in the broad sense actually works really well. One reason is explained in Kickstart, selling better tools rather than giving them for free ensures that the recipient will use them (80% as opposed to 30%) to become improve their income and become self-sufficient. This is more the distributism model of capitalism than corporate (not the catholic part, but the idea summed up by "The problem with capitalism is not too many capitalists, but not enough capitalists"), but it's still capitalism which works well in general. And it's not particularly volatile compared to older economic forms, we forget now but famines (the closest to an economic breakdown feudal societies have) used to be incredibly common, occurring at least once every 2 generations.
We denigrate it because it isn't perfect, but one lesson of the last 200 years is that capitalism (especially coupled with democracy) in the broad sense works far better than the alternatives. "a market economy is to economics what democracy is to government: a decent, if flawed, choice among many bad alternatives." The debate should not be between the various different economic systems (communist, mercantile, guild based, feudal + manoral, capitlist, etc) but what types of capitalism work best and in what mixture. Should we encourage cooperatives like Eureka's future, that can fit into the market system we already have? what sort of government regulationis useful and how should it be implemented? What areas aren't aproppriate for private organisations (evidence points to health care and education for one, but what others)? of the various types of capatilism, what mixture makes sense and for what areas? how global should it be (relates to tariffs and such)? and so on. We already did the experiments to figure out which broad economic system works best, the goal now is to optimise and improve that system.
Feudal systems tend to have strict controls on the movement of peasants (who made up most of the population), like police states control peoples movement. One way was through basic laws, in England a serf became free if he evaded capture for a year and a day, that restricted movement, marriage, access to work and other similar activities. The other way was through economic structures, one of the function of guilds was to limit the influx of peasants into cities (because living in a city was better than not), and to preserve the massive advantages given to nobles.
Mobility equals wealth, an example of this in practise is asylum seekers, the ones we get by boat aren't the poorest (nowhere near that) because the poorest can't afford to get on boats and are stuck in giant refugee camps or are stateless. So one way to stop movement is to destroy wealth, or stop it from accumulating in the lower classes.
Nobles consistently shaped the economic and political structures of their societies to benefit them at the expense of everyone else. Having complete legal immunity to taxation was a common perk (the Dutch didn't have that perk and they got a trading empire), which considering that nobles generally owned 60-80% of the land helps explain why governments didn't do much in civic terms until the late modern period, along with exclusive access to upper level religious, military and political (like judges, also sheriffs were nobles for this reason) positions. Most civic improvements were done by private individuals for various reasons (Rome traded political influence for civic goods), but modern history shows that isn't the best way.
One of the things people forget is that most kings, aristocrats and emperors are horrible to mediocre rulers, only a minority are actually any good (like Frederick the Great) and have the interest of those they rule at heart. They normally want to enjoy power and all the benefits it brings; which might be sleeping with lots of women (the Ottamen or Chinese harems were institutional forms of this), drinking lots of wine (one Khan made a promise to only drink one cup a day, so he built a cup the size of a large bucket) or becoming so fat that a special device has to be built to lift the monarch out of his throne. This is one of the big reasons most pre-modern civil wars are more about who rules than about freedom or political structures. Modern politics forces them to at least pretend to care about the ruled and that works a whole lot better. What's happened is a political form of the hedonic treadmill, our politicians/rulers have gotten better, but that has simply raised the standard,
Africa is likely going to be a good test of theories
Africa has some of the youngest (Kenya is only 50 years old, Egypt is 80) and least stable governments. It is also the poorest part of the world and thus the least able to cope with climate change and fossil fuel depletion. So Africa is likely going to be the first continent to get cut off from the globe and suffer most of the problems of overshoot.
Which makes Africa a good place to watch since it could easily be where quite a few events happen first. This its a a place where theories can be tested.
So how will indications that stability is approaching go?
Improvements to governance?
And then there is China's growing influence and presence in Africa along with its ongoing transport issues and natural resources.