Truth is, you have to go a long, long way back to find the roots of inequality. Agriculture. Pre-agricultural societies have very little inequality.
However, capitalism can initially produce greater inequality. If capitalism is entirely free, that won't last. But as Adam Smith wrote, you can't find three businessmen meeting socially, without some plot against the public good. Businessmen hate uncertainty and competition, and do what they can to reduce it.
So it's complicated.
NAFTA mainly disadvantaged unskilled workers, whose wages fell and who were competing for fewer such jobs. But this is the effect of free trade and market forces. We shouldn't be making many things that require only unskilled labor. Doing that would simply increase prices of those things, and so make all Americans poorer.
We need to do the things that require higher skills, things that we can competitively sell in the world.
The huge challenge is to prepare workers for that 21st century American economy.