"Money buy assets & assets produce more money to buy more assets... so on."
That is accumulation not concentration.
For concentration to occur there must be either an increase in the percentage of newly created wealth going to a minority or a transfer of existing wealth from the majority to that same minority.
An example.
"The rich don’t just have more wealth than everyone else. The bulk of their wealth comes from different — and more lucrative — asset sources, as the Federal Reserve’s Distributional Financial Accounts data shows. America’s top 1 percent, for instance, holds more than half the national wealth invested in stocks and mutual funds. Most of the wealth of Americans in the bottom 90 percent comes from their homes — the asset category that took the biggest hit during the Great Recession. These Americans also hold more than three-quarters of America’s debt."
