Via Kevin Drum, a quick look at the share of national wealth in the hands of the top 3% of Americans, as compared to the bottom 90%:
The data comes from the Federal Reserve´s 2013 Survey of Consumer Finances. In 1989 the top 3% were already ahead by 11 points. 24 years later, the distance has climbed to 30.
It is important to stress that this is something fairly new. The United States was in 1970 one of the most egalitarian societies in the developed world, with an income distribution not that different from what we could see in Germany or Sweden. Starting in the early eighties things suddenly changed, and the US became a remarkable outlier in this regard, with only the UK coming even close. The rise of inequality in the United States was certainly not inevitable, by any means.