Capitalism has an inherent flaw caused by the fact that those with large amounts of capital are better able to draw more capital out of the system. This implosive pressure results in more money in the hands of fewer people over time.
Since Reagan the barriers to that accumulation have been steadily lowered. And thus we end up with a handfull of people holding the vast majority of the money. But it's very hard to say at what point the system actually becomes unstable. I suspect that it won't collapse from internal failure, but will become increasingly fragile to external shocks.
Jay