I think about this all the time.
I believe it arises from an interaction between individuals and the surrounding culture and institutions.
Let's assume, a priori, that everyone is trying to maximize their "success". This doesn't necessarily mean purely selfish greed, but more an observation that there's a natural incentive to take care of ourselves and our own and that we will naturally try to figure out how to get there.
The "get there" part means navigating the social environment and institutions that surround us. We aren't living alone on a desert island where our options for survival are purely physical. Most of our interactions and choices are around other people and social systems. So when we seek success, we are pathfinding through the rules, norms, and ethics of the culture we're embedded in.
What kind of path do you take? In a culture with low corruption and high institutional trust, the most efficient way to acquire resources and stability is by playing the game honestly and cooperating in good faith with others. If we all do the right thing, we all win. Overall efficiency goes up and that benefits all of us.
In institutions with low trust and high corruption, playing by the rules and attempting to cooperate leaves you open to exploitation because your peers aren't doing that. You'll get screwed.
Now the fun part is the feedback loop between individuals and institutions. A culture is just the collective choices of all of the individuals in it, so every move we make in the game is also an act of defining the rules of that game.
The greater trust we have in each other, the more efficient the system gets and the better it is for everyone. But by that exact same token, the easier the system becomes to exploit and the more attractive it becomes to bad actors. The optimally efficient society is also the perfect honeypot. So as we seek greater trust and efficiency, we also directly incentivize deceipt and corruption.
Going in the other way, as a society gets more corrupt, it becomes less and less efficient. It's hard to get anything done when every single action requires several rounds of negotiation at gunpoint because everyone is presumed to be an adversary. So as a society becomes less trusting, it loses the ability to compete against other more efficient, trustworthy societies.
What I think you see is that as a larger society's institutional trust falls, within that society new pockets of trusted cooperating subcultures arise. Since those are more efficient than the larger society, they tend to grow and outcompete. But people in those pockets don't trust outside of that subculture, so you end up with the inefficiencies of mistrust and adversarial interactions at the boundaries between these groups.
Eventually a group might win and continue to grow, but the bigger it gets, the harder it is to maintain cohesion and trust across all of it. So eventually its overall trust fades but then new pockets of trust appear inside it.
This sort of slow boiling foam of fading trust and growing bubbles of cohesion is, I think, fundamental to human sociology.