Did we really change?

I think I have known enough history to understand what humans did to each other over last 3000 years. Seen enough war movies to understand the feelings of people who are involved in killing or get killed.

From the beginning I have a doubt, why do we always blame the leadership for what a country and its people did to other country and its people? There are lot of instances in our 3000 years of history where a country attacked other country and killed people in other country without any regard to human life. There are instances when one race thinks they are supreme than others and started killing all other people(in millions).

In those cases, who is wrong? Country is nothing but people and who is running it. One person can not do anything to any other country. He/She has to do it through people.

People still exist, and if we think we have not changed, then those instances can occur again and again. If we think people have changed, I would like to see one real proof of it. I have not seen it yet.

How long it will take for one particular set of people start believing that they are superior race compared to others?