According to Piketty's Capital in the Twenty-First Century, which despite being 700 pages is incredibly readable for people without any more than basic historical and economic knowledge, the top 1% in the US has an equal share to what they had in the Gilded Age. And Piketty discovered that nearly a decade ago.

Like much in economics, there is debate as to why it narrowed. I'm only going to discuss Piketty's argument since it is one of the better ones to incorporate copious historical data. In short, the rate of return on capital grows faster than the economy and wages, this is a point Marx hit upon and Piketty proves it continues to be true today. This means that, lacking a concerted government effort towards its reduction/redistribution/elimination, those with capital will always become richer than those without. Since capital can be inherited (unlike wages) in an ever-snowballing expansion of wealth, the wealthier always become wealthier unless an outside event (e.g., destruction of capital via war like Europe in WWI and WWII, government policies like high capital gains tax and inheritance tax in the US and UK in the mid-XX century, etc.) intervenes. As you can guess by the previous sentence, according to Piketty, there was a purposeful effort by the US towards the goal of elimination of inherited wealth.

It is a bit more complex than this though, but they are minor and of little relevance to most non-economists. Also, I should note, capital for Piketty is more expansive than the traditional Marx-derived definition.