What is happening in places like Bosnia, Rwanda, Sudan, Israel, the United States, where people kill each other with casual bravado?
Certainly some killers are acting out their own abuse as children. A particular political, religious or economic situation might be pounced upon as an opportunity for the release of rage. The psychopath sweeps lesser but like souls up in the frenzy, granted permission by a situation of chaos to act out. If the abused are in authority others go along or risk becoming victims themselves.
As children we learn to limit who we identify with to those of our own family, neighborhood, city, nation, race, class, religion. The them/us mentality is fertile ground for national, ethnic or religious conflict, aggravated by the abusive scenario and exploited by unscrupulous leaders.
Rulers try to direct the process, getting us to think of allies as tentative members of the home team, and rivals as not quite human. Rulers will naturally find dangerous those who advocate expanding identification beyond the state to the whole species. A people who considered all human beings family might limit a ruler's capacity to drop bombs, to dominate economically, or expand territorily.
Now how do we get directed into limited identification? In the U.S. the rulers behind the throne are those who finance elections. Naturally the well-heeled give to those who will do their bidding and withhold from those who will not. Since campaigning is incredibly expensive, anyone running for office unable to buy television time, newspaper ads etc; can't get the visibility to even enter the discussion.
Corporations and wealthy individuals, the prime financiers, can be counted on to support those who will serve their interests, who will maintain and expand their wealth and power. Since this same class owns the major media (television networks, daily newspapers, radio stations) they also largely control the debate. They will certainly not hire someone who believes that capitalism is inherently unfair, stacked against the mass of people in favor of the few. No, your career prospects are definitely improved if you think that capitalism is humankind's greatest creation.
If you for example thought that no one should own more than 500 acres of land, that income over $300,000 should be taxed at 100%...stuff like that. Well you need not apply for editor of the New York Times, columnist for the Atlanta Journal Consitutuion, CBS anchor etc; no matter how great an editor or writer or anchor you might be. So to those who are hired those ideas would seem completely off the wall, not serious, not worthy of discussion. They are excluded, not with a feeling of censorship but with a sense of responsibility.
When all the assumptions a population encounters, everywhere they turn, conform to those of the rulers then on that rare occasion when a non-conformist idea arises it seems quite crazy, readily dismissable. What is being described here is a subtle propaganda system. It is aimed primarily at those who are invested in the system, the middle and upper classes. For the rest there is stupefying television, sports, and other diversions - the occasional, carefully limited election.
There are differences among the rulers and those differences are mirrored in the media. In the eighties, some columnists thought we should send U.S. Marines to Nicaragua. Others thought we should fund mercenaries, the "Contras". Still others, the "liberals", thought we should just crush the Sandinista government economically. But virtually no columnist in the major media took the position that Nicaragua had an elected government and should be supported in its attempts at democracy, land reform, redistribution of wealth. Such a view was radical, not worthy of discussion, even unthinkable to many.
Also not included in the options toward Nicaragua was the possibility of non-violent conflict resolution, a meeting to seek a solution that benefits both parties. Washington always claimed to be trying to push Nicaragua toward democracy but beyond the rhetoric was a fear of democracy, fear of the example of a successful equitable society. Other countries might get ideas. People in the U.S. might get ideas. The upstart must be nipped in the bud.
This meandering attempt to address the opening question concludes with a tentative answer. Limited identification is one of the major factors that perpetuate war and injustice. Acquiring this trait is a matter of course in a highly indoctrinated society and it becomes lethal when exploited by those who wish to dominate others. When our primary loyalty lies not to any particular country or religion but with the whole human family and the well-being of the natural system that makes life possible then the killing will, at long last, stop.