Why Is This Happening? With Chris Hayes

What can soil tell us about election results? After every election, analysts pore over piles of data in order to better understand political trends. But what if a better place to search for answers is the ground beneath our feet? More specifically, whether that soil was conducive to crops worked by slaves over 200 years ago?Listen to Maya Sen and Matthew Blackwell trace southern racial conservatism all the way back to glacial deposits. Their new book, "Deep Roots", studies the swath of America where slave-based economies thrived as a result of nutrient-rich soil ideal for growing cotton. Hear them uncover the tangible legacy of slavery that continues to shape today's political life.Email us at WITHpod@gmail.comTweet using #WITHpodRead more at nbcnews.com/whyisthishappening