  Many democratic societies have become more politically polarized, with the
U.S. as the main example. The origins of this phenomenon are still not
well-understood and subject to debate. To better understand the mechanisms
underlying political polarization, we develop a mathematical framework and
employ information-theoretic concepts to analyze empirical data on political
polarization that has been collected by Pew Research Center from 1994 to 2017.
Our framework can capture the evolution of polarization in the Democratic- and
Republican-leaning segments of the U.S. public and allows us to identify its
drivers. Our findings provide empirical and quantitative evidence that
political polarization in the U.S. is mainly driven by strong and more
left-leaning policy/cultural innovations in the Democratic party.
