Steven Pinker 3: The surprising decline in violence

Steven Pinker at TED2007
The surprising decline in violence (transcript)
Summary
The speaker tells us that no one really knows why violence has declined, however, he has four explanations that have some grain of plausibility.

There is a policy that people will retaliate savagely when they are invaded. A deterrence power is working. 1)

People have known about the value of life 2) and the value of others. 3)

Our sense of empathy is improving. 4)

People just got sick of the carnage and cruelty. This seems to be that it outstrips behavior by the standards of the day.

I was shocked by one example of his third explanation.

It's about dropping bombs on Hiroshima, Japan in the World War 2.
When I was a student, I learned that l had to be remembered it as only real fact without discussing.
It was only a sad event, and then l thought it never happened from now.
However, I’ve read from some articles that Japan started the World War 2 and didn't stop it, thus the bomb was inevitably dropped. My head was full of inevitability, it's necessary and Japan should apologize. However, this article tells that Americans should not bomb Japan because we’re a country that built minivans that Americans used. It's said probably after big earthquake and tsunami, 3/11.

I don't know what I was shocked at clearly, l haven't gotten an answer though l think that we, Japanese people, have to not only learn about our histories but also discuss those more.

The speaker tells us that people couldn't acknowledge past culture because of guilt.

However, media can announce many things quickly in our modern world. It leads to misunderstanding, but it sometimes helps us.
It wouldn't be unnatural to change our thoughts, it might not achieve answers, no one might know it and there wouldn't be right answers.

The speaker’s conclusion is that we shouldn't discuss why there is a war but we should discuss why there is peace. We have to train our imagination to trade places with someone else. It increases our moral consideration to other people.

Words in this story
violence /noun/  brutality, savagery
plausibility /noun/ believability
retaliate /verb/ take revenge
savagely /adv/ brutally, viciously savagery /savijrē/noun/
deterrence /noun/ determent, intimidation
acknowledge /verb/ accept or admit the existence or truth of.
Enlightenment /noun/ the action of enlightening or the state of being enlightened.