What Causes Genocide?

I have heard the term "genocide" only a few times in my life. When I think of the word genocide, I instantly think of mass murder and the Holocaust. I think genocide starts when people believe that getting rid of certain groups of people is the only "sane" or "pure" way to live.


I have a few questions regarding genocide: I recall that the Holocaust was a major genocide targeted at "unfit" groups of people, such as Jews and disabled people. Is hate and prejudice a factor in the causes of genocide? When I think of genocide, I think there must be a reason to kill masses of people; why would people kill people for no reason at all? Also, has genocide become obsolete, or is genocide still prevalent today?