There are three reasons why violences has relatively declined in the world. The world has become more educated, is taking a long overdue break from violence, or it been pussified by the abundance of breeding leftist pussies.
I'm not buy this crap about better angels of our nature crap. We're aren't competing for material and territory like we use to and if the inequality of this world gets any worse you will see more bloodshed and fight for resources in no time. I just hope I am not around for the spring of WW III.