Mortality determines society. By this I mean that the function describing mortality rate by age in humans acts as a filter to determine the sort of societies that can exist and support themselves. A high mortality rate reduces the range of societies that can exist. The mechanisms at play in this relationship are economic in the broadest sense: a mix of population growth, division of labor, effectiveness in recording and transmitting knowledge, time preference, establishment of sufficient capital for more than just subsistence living. Consider the difference between the late paleolithic era and classical Greek civilization, for example, and think on why they are different.
In terms of mortality, the immediately noticeable difference between the classical era and prehistory is an upsurge in the number of people who reached old age - a reduction in the omnipresent violence between small groups, and a marginal improvement in medicine. As a general rule you don't find the bones of old people in early human archaeology: so few of them made it past 40 as to be close to absent entirely as a class. Mortality rates in classical Greek and early Roman times were horrific by modern standards, but enormously improved over those of prehistory.
Thus as a consequence there were both old people and a certain expectation of reaching old age - which means a rise in planning ahead and an increase in available capital. A longer vision breaks through destructive cycles of economic behavior that take place on shorter timescales. As one example, people cultivate their property more effectively if they think that it must last for longer under their stewardship, more readily resisting short-term gains that come at the cost of long-term gains. This incentive has operated throughout human history, whenever average life spans rose. A later example can be seen in the simultaneous rise of life span and economic well-being in 17th and 18th century England:
If life cycle inspiration was present in rural England in the 18th century, farmers who were becoming aware that old people were gradually living for longer periods must have been more concerned about their own means of subsistence in the future. This may have been an important stimulus to reduce consumption, increase savings and take into account longer horizons.
Various destructive cycles of poverty to wealth to poverty exist for all time scales of human behavior and all population densities. A greater expected span of life doesn't make them go away entirely, but it does mean that more people will be around to suffer the consequences of ill-thought action - and as a result, endeavor to understand and avoid the acts that lead to suffering they see in others. Don't eat your own seed corn; be the ant rather than the grasshopper; don't cut down the whole forest; engage in trade rather than slavery; shun destruction in favor of construction; allow the merchant class to exist; and so forth. You might see the commonality here: it is restraining the urge to obtain short-term gains that harm the prospects for long-term gain.
One important thing to note is that all historical progress in expanding the range of possible human societies has come about without greatly altering the maximum human life span. It was possible to live to more than a century without modern medicine and in the presence of pervasive disease and violence - that outcome was just enormously unlikely for any given individual. Improved mortality rates led to a growth in the number of old people and their influence.
I submit that this largely unchanged outer limit to life span is why we can look back on thousands of years of politics to see the same patterns repeated over and again. Regions rise and fall. Empires form and decline. Countries become wealthy and then poor. Democracies slide into authoritarianism. Currencies are steadily debased and destroyed. Known and enumerated forms of governance arise over and again, and fail in the same ways each time. The patterns repeat because throughout history expectations regarding the outer limits of personal stewardship and responsibility remained set at something less than a century. It is that span of time that drives choices made between cultivating future growth versus squandering it for present advantage - and even drives whatever incentive exists to understand that you are taking one of those paths rather than the other.
After all, economics as a professional body of knowledge and theory only really evolved into the forms we'd recognize today in the wake of 17th to 18th century gains in longevity, after the rise and fall of physiocracy as a flawed means to explain the wealth or poverty of nations and how that related to human behavior.
Just as paleolithic hunter-gatherer groups were stuck in their own limited range of sustainable human societies, their choices and cultural evolution over time driven by high mortality rates at all ages and the near absence of elders, so are we also stuck in our own, larger range of possible societies. Our present span of life limits us to what we see. Where wealth, freedom, and the rule of law necessary to create wealth arise, they corrode over time as successive generations forget how and why their good fortune came about: they eat their own seed corn. We can see this happening in the US, somewhere past the mid-point of the process, and all somewhat analogous to the decline of the Roman Republic, at least insofar as root causes are considered: successful republics have a way of falling into empire and authoritarian rule, accompanied by massive military and welfare spending. Bread, circuses, and the legions.
All humans of our maximum life span and adult mortality rates low enough to allow for societies of cities and writing have found themselves trapped within the wheel of time I described above: the rise and fall of polities that takes place over centuries, poverty to wealth to poverty, or tribes to civilization to tribes. It is the consequence of our dominant short-termisms; where our time preference fails the test; where we squander our own potential.
The human condition has been bounded in this way for a very long time indeed, since the first cities arose more than 6,000 years ago, but it will not continue for much longer. In this age of biotechnology the transition from age-bounded life spans of a century to accident-bounded life spans of thousands of years will happen in the course of mere decades. Entire populations will stop dying as therapies capable of repairing the cellular and molecular damage of aging become widely available. Degenerative aging will become a controlled medical condition, warded and defeated like smallpox and others in the past century.
The wheel of time will be broken. Those who stand at the beginning and the height of empire will be the very same individuals who must also stand at its decline: their horizons will extend, and so the shape of empire will be quite different, if it comes about at all. How will this play out, this grand restructuring of all the incentives that lurk at the base of human societies? What new forms of society will emerge as possibilities given widespread radical life extension? These are open questions: the changes to human life span that lie ahead are dramatically different in character to those that have occurred in the past. The gulf in mortality and life span that likely lies between us and the humanity of the 22nd century is far greater than that separating paleolithic hunter-gatherers from the classical Greeks. Further, it will occur in a comparative eyeblink - a single generation will stand with one foot in each world.
Yet the wheel of time will be broken, and this seems to me to be a good thing.