Thomas Pikkety's books (Capital in the 21st century, etc) are an excellent and comprehensive data-driven analysis that examines the state of inequality today, all over the world, compared to centuries of history.

For those not in the mood to read a 700 page tome, listen to his lectures (e.g. https://www.youtube.com/watch?v=3ofjozfEr-U, https://www.youtube.com/watch?v=1i5x_MrTuYs). I promise it's worth it.