In his talk on income inequality, Thomas Piketty discusses the lessons he learned studying the history of wealth and income distribution over the last 15 years. His main thesis is that in the long term, there is a tendency for the rate of return capital to exceed the economy's growth rate, which then tends to lead to a high concentration of wealth. However, the speaker disclaims that this is not the only important force in the dynamics of wealth distribution. He warns there are lots of other factors involved and more data is necessary.
Most of data mentioned in the talk on income inequality is from The World Top Income Database. The speech further outlines other facts gathered from this information. First, there's been a reversal in the ordering of income inequality between the United States and Europe over the past century. This is due to changing supply and demand for skills, more unequal access to skills in the US and globalization among others. The speaker also states wealth inequality is always a lot higher than income inequality and it is also less extreme today than a century ago, although the total quantity of wealth relative to income recovered from World Wars and Great Depression.