Global Trends Versus Local Politics: what caused the increase in inequality in industrialized countries?

I have found on Twitter this video of the change in income distribution in the United States of America from 1971 to the present.

Watch the income distribution in America change pic.twitter.com/Rtun7mN6bN 

— Conrad Hackett (@conradhackett) April 27, 2017

That's interesting and a good starting point in understanding the US political economy (without reading Trump's twitter feed). Another interesting reading is Enrico Moretti the New Geography of Jobs (https://www.gsb.stanford.edu/insights/enrico-moretti-geography-jobs). The question is left in my mind is how much these dynamics are the product of technological change and globalization and how much is the product of policy choices that determined the unequal distribution of the cost of adjustment.