What is unusual (I think) about the Jewish Holocaust is that it wasn't part of a conquest. Jews were very well integrated into German society, and had never been at war with it. Any other similar cases?
Maybe a more salient example than my integrated Native Americans: Protestants v. Catholics.
In certain circumstances it was simply war and/or strife.
("simply")
But, in situations where both groups were fully native, there were situation where one group would try to eliminate the other through legislation, deportation, and also extermination.
A monthly thread for posting rationality-related quotes you've seen recently (or had stored in your quotesfile for ages).