is that concentration of ownership of the nation's resources in fewer hands is increasing radically. This is not going to change during the next several years, and probably will not change for many, many years to come. The markets or economics do not explain this. This is happening solely because of politics.
Various wealthy parties have bought exceptional influence during the past 20-30 years in the political process, and this has resulted in an extraordinary, contrary-to-market-forces shift in concentration in American wealth.
A considerably open international economy has also contributed to this. A small number of people make hoards of money buying in extremely low-income regions of the world and selling in high-income areas of the world. This doesn't just contribute to extreme wealth concentration, it also lowers wages in the 'high-income' markets where this stuff is sold. This is much more economic in nature - but it is also political. Greater international trade regulation would inhibit wealth concentration while slowing any related decline in wages and salaries of most.
So - understanding economics won't lead you to correct conclusions about income in this country, unless you open the economic model to the markets in politcal corruption.