I'm currently studying a unit on massacres and genocide. Cheery stuff but unfortunately, such phenomena is endemic to human history. The idea of the subject is not really about a body count but rather, to get an understanding of the legal concepts and why such terrible events occur. The most well-known instances such as the Holocaust will be part of the course but also consideration of what went on in ancient times. Ancient empires including that of Athens and Rome were not averse to mass slaughter if it served a political purpose.