system
A chat on subreddit /r/PoliticalCompassMemes
human
"Who Really Cares" by Arthur Brooks was a huge one for me.  I grew up surrounded by liberals in a very liberal city, so getting to see actual evidence showing that "Republicans hate poor people" was total bullshit was enlightening.

"How Capitalism Will Save Us" by Steve Forbes.  Though holy shit it has probably the worst title of any book I've ever encountered.

Basically anything by Thomas Sowell.

"The Three Languages of Politics" by Arnold Kling.  Just a really good book in general for understanding why people of various political stripes come to the conclusions they do.
gpt
Thomas Sowell has a way of making things easily accessible. I thought he was just brilliant and my economics degree helped me understand him but then some friends of mine had read his stuff and I realized he's easily digested by non-economists. 

Thinking Beyond Stage one is one of my favorite Sowell books because once you understand it you'll never fall for bullshit like the "clean air and water bill" because you'll immediately ask "and then what happens?"