Look up the societal collapse of Rome in particular. It's one of the most named and covered anecdotes. A few other societies follow similar patterns, internally collapsing and being taken apart piece by piece rather than aggressively overtaken. Wikipedia[0] names several societies (I don't keep sources at hand to my own discredit).
It all has to do with incentives and the role of men in societies which to some degree still apply today. Stop giving men incentives to have families or any other reason to care about younger generations, and they stop having a reason to care for the future. Don't give them an incentive to care about the now (wives, partners, comrades), and they stop having a reason to care about the now.
Not having people care for the future is a great way to make them live their lives as short-sighted and hedonistic* as possible, which further affects their reason to care about the now beyond themselves. Not having people care for the now is a great way to incentivize inner conflict and have a party rise to fill the gap.
*: Hedonism on its own has a whole slew of other problems I'd rather not get into detail with, but for the sake of comparison, online dating apps' meat market approach hasn't exactly helped younger people obtain more satisfying relationships.
Societal collapse is probably something most people desire to avoid, and if the large numbers of disaffected men are the 'canary in the coal mine' and symptomatic of a weakened society, then we as a society also want to come up with solutions to ameliorate that particular suffering as a part of strengthening society as a whole
The best thing about the fall of Rome is how you can read literally anything into it
too many soldiers
too many men, not enough solders
too many immigrants
not enough immigrants
immigrants didn't integrate
immigrants integrated too much
not enough defense spending
recession from too much defense spending
lack of scientific knowledge
proto-technocracy instead of realpolitik
i.e. take your pick of
too much like today
not enough like today
as well as
the worst thing to happen to civilization
not actually that bad
Honestly, my favorite explanation is that gold currency is a ponzi scheme that forced the roman empire to conquer more and more gold bearing land until its territory was so large that it was difficult to defend while simultaneously invading new territory. The moment they failed to conquer an ever growing mass of land, they had to pay the army while all the wealthy people have hoarded gold and kept it out of circulation which destroyed the medium of exchange function of money and therefore forced Romans to issue additional coins with less gold to pay its soldiers as hoarded gold coins do not pay any taxes.
Most people interpret inflation as obvious government mismanagement, I interpret it as an inevitability because of the inherent conflict between medium of exchange and store of value caused by using gold as currency.
Saved money that is used as a store of value interrupts the circulation of money which then stops the payment of taxes which then forces the government to find a substitute for the loss of tax revenue. The answer is to separate the medium of exchange and store of value function into two separate "institutions". Cash is not a store of value, banks delegate the store of value by giving loans to producers of value i.e. companies and entrepreneurs. If you just save cash/gold, there is no guarantee anyone is going to produce value in the future. You are basically speculating that there are going to be people in the future that will gladly take your gold and then people act betrayed when that speculation didn't pan out.
It all has to do with incentives and the role of men in societies which to some degree still apply today. Stop giving men incentives to have families or any other reason to care about younger generations, and they stop having a reason to care for the future. Don't give them an incentive to care about the now (wives, partners, comrades), and they stop having a reason to care about the now.
Not having people care for the future is a great way to make them live their lives as short-sighted and hedonistic* as possible, which further affects their reason to care about the now beyond themselves. Not having people care for the now is a great way to incentivize inner conflict and have a party rise to fill the gap.
*: Hedonism on its own has a whole slew of other problems I'd rather not get into detail with, but for the sake of comparison, online dating apps' meat market approach hasn't exactly helped younger people obtain more satisfying relationships.
[0]: https://en.wikipedia.org/wiki/Societal_collapse#Examples_of_...