The stat I've heard (in soundbite form; I don't have solid data for this) is that inequality
within countries is rising across the board, but inequality
between countries is falling. In other words, a rich Chinese person is now much richer than a poor Chinese person, a rich Mexican is now much richer than a poor Mexican, and a rich American is much richer than a poor American. However, a rich Chinese person or Mexican is now almost as rich as a rich American, while a poor American is now nearly as poor as a poor Mexican. And a rich Chinese person is significantly wealthier than a poor American, while it used to be that poor Americans were significantly wealthier than even wealthy Chinese.
There's plenty of anecdotal evidence to support this, eg. the richest person in the world was Mexican from 2010-2013, and it also makes a lot of sense when you consider how globalization works.