1.) Humans productive enough to create a surplus.
2.) The idea to reinvest the surplus with the aim to increase productivity even further to open up a way into a better future for themself and their children.
3.) A random distributed (over time and over population) individual success rate (return on investment) in achieving this goal.
These three ingredients alone are enough to drive a process of steady wealth concentration into the hands of a few. The rate with which the concentration progress proceeds, depends primarly on the spread (sigma) of the individual return rates.
Even with in average (over the population) negative return rates concentration rises over time.
Economics that don't understand this and politics that increase the spread (sigma) of the return rates, driven by the belief, that a wider spread creates a higher common wealth, are accelerating this effect. The net results are not only wealth concentration, but also progressing concentration of firms and banks. And when you assume this concentration process valid and working also on money, it explains the escalating instability of banks after a certain period of time as well.
If you are seriously interested in the mathematics behind this sneaky thing, you may want to take a look at:
When we understand this and recognize, that this is not only causing instability in our financial system and our societies, but undermines the very foundations of modern democracies, we are free to choose and can apply strategies to stop it with civilised and legal means. If we fail to do so, this will further destroy our financial systems, our economies, the cohesion between people and finally peace.