Dogs
This question is one of the central issues of the human race. It is not new, but became critical to our survival in the 20th century with the rise of powerful central states, the development of propaganda through mass media, and the application of industrial technology to mass murder. These factors changed the equation drastically.
The most documented example is Nazi Germany of course, though as Andrews points out there were many others in the last 100 years. The best film documentary of World War II was produced by the BBC in 1973 -- The World at War. It is available from Netflix. Disks 8 and 10 are outstanding for showing daily life in Germany, the rise of Nazi control, and how the holocaust was conducted. The answers are all there if you can stand to look. Then ask yourself if you see similar actions taking place today. http://movies.netflix.com/Movie/The_World_at_War_Collector_s_Edition/70102599?trkid=2361637
Thanks for introducing me to Andy Andrews. This interview of him compliments the video you posted. I can't get it to embed.
http://michaelhyatt.com/how-do-you-kill-11-million-people.html
Travlin
PS - The World at War will never be equaled. Their timing was ideal. They interviewed many participants and players while their memories were still vivid, but events far enough past that they could talk about them. It is in a class by its self.

One of the many books I read during my time away from the site....
Written by Andy Andrews, fantastic author IMO. He wears his faith on his sleeve so for those of you who may get your bowels in an uproar over that, you have been forewarned.
Read it if so inclined and form your own opinions.