The top chart shows the amount of income the richest 10% of Americans have gotten historically in relation to the other 90% of all Americans. Note that from around the end of World War II to about 1980, the percentage of the nation's income received by the top 10% was between 30%-35%. And the other 90% received between 65%-70% of the national income. It was not an even split in income (and never could be in a capitalist system), but it was acceptable because all Americans were getting at least some share of rising productivity.
But Ronald Reagan was elected in 1980, and with the help of his Republican cohorts (and some blue dog Democrats), he instituted an economic policy dubbed "trickle-down" (because it was based on the theory that if the rich were given more, some of that economic wealth would trickle down and everyone would benefit). But no money trickled down, and the policies just made the rich even richer while everyone else suffered.
Note that the share of national income for the bottom 90% of Americans began to decline after 1980, and now rests at about 49.6% of the nation's total income ( a drop of around 20% in their share of national income). The opposite was true for the richest 10% of Americans. Their share of the nation's total income grew by about 20% (rising from between 30%-35% to a current share of 50.4%). That's right -- 10% of Americans are gobbling up more than half of the nation's total income, while 90% of Americans get to divide less than half among them.
And it's not getting any better. Another report has shown that in the "recovery" from the Bush recession (in the years between 2009 and 2012), the top 1% has received 95% of the increase in income, while the bottom 99% got only 5% of the increase in income (and you can bet that 5% was not shared with anyone in the bottom four quintiles (bottom 80%). Not that in the bottom chart above, the income for the bottom 80% of Americans has dropped since the "trickle-down" policies were instituted. The only quintile with an increase in income was the top quintile (top 20%) -- and most of that was received by the top 5%.
This is why we now have the biggest gap in wealth and income between the rich and the rest of America since before the Great Depression. And since the congressional Republicans have blocked all attempts to return the country to a sane and fair economic policy, that gap continues to grow even larger with each passing day. This cannot continue indefinitely without completely wrecking our economy. But the corporation and the rich (and their congressional lackeys, the GOP) don't seem to care about the future. They are only interested in squeezing every dollar possible out of today.