The video below shows a version of Stanley Milgram's classic experiment looking at "Obedience to Authority". What you will see is why decent people are prepared to administer potentially fatal electric shocks to a perfect stranger; just because a man in a white coat tells them to do so.
This has wider implications. It proves that a person in authority can manipulate ordinary people to commit gross acts of violence. This goes someway to explaining (but not condoning) the behaviour of the Nazis during WW2. It also shows that extreme dictatorships can also manipulate people and armed forces.