Wealth concentration has been a deliberate US domestic policy for decades. This is, to a large degree, separate from the stability of our currency or military protection. It's the stated intent and logical result of relaxing taxes on the rich while enacting policies designed to hurt the working classes (e.g. reducing union power, not indexing minimum wage to inflation, refusal to address healthcare & housing costs, increasing fees at public universities, cutting existing safety net programs, etc.).
Concentration of wealth is a choice. America is a very rich country and has not always chosen to distribute our wealth this way. Other countries make different choices. We are also allowed to make different choices.