The broad outlines of the Holocaust are generally known, but these two books offer a deeper understanding.    Anatomy of a Genocide by Omer Barton shows how mass killing can take root among neighbors.  The village of Buczacz  in western Ukraine was once   Roman Catholic Poles, Jews and Orthodox Ukrainians who had lived side by side in relative harmony.  Before the world war was over, first the Jews and then the Poles were massacred. Author Barton takes apart the rivalries and jealousies that led to this horrific falling out.      The Death Marches by Daniel Blatman looks at the final days of the holocaust, in which the Naiz closed camps in the path of advancing armies and transported the prisoners deeper into Germany.  One of his findings is the culpability of  German civilians in the mistreatment of the captives.