Why do pogroms occur in some localities but not in others? This question has long puzzled scholars.  With a focus on the wave of pogroms in Eastern Poland and Western Ukraine that occurred in the first weeks after the Nazi invasion of the Soviet Union, Professor Kopstein shows that pogroms are only weakly correlated with Polish and Ukrainian nationalism and Jewish support for communism.   Instead what matters most  for the occurrence of pogroms are pre-existing political and demographic tensions, especially Jewish support for ethnic parties.  After discussing these conditions, Professor Kopstein will note what this conclusion means for Polish and Ukrainian wartime culpability and the broader conditions under which pogroms are likely to occur.