Need for Violence

A couple days ago, protestors came to Chicago because there was a North Atlantic Treaty Organization (NATO) conference taking place with a lot of the world's leaders.  What I found particularly interesting was how the media covered this event.  I flipped through multiple news channels during this time that were all covering the protestors, but not one mentioned what was taking place at the conference or what the protesters were protesting.  The only thing that was ever covered was the violence, or lack of violence for that matter, that occurred.  For example, take a look at this snapshot of the CNN coverage below:

Almost every other news station, like CNN, mentioned and tried to cover some sort of "clash" that took place between the police and the protesters, and then after is was all done and they realized there wasn't any violence to report, they'd all say, "Well the Chicago police did a very good job," seeming slightly disappointed that they couldn't make a big story out of it as they clearly planned to do.

This type of news coverage didn't just occur during this event, it always happens.  All the time, the news reports violence only without ever really telling the reasons behind it like they did here.  What was the NATO Conference for?  What were these people protesting?  To be honest, I still don't really fully understand despite looking and asking people, and nobody can tell me for sure what this is all about.  All I've heard is that the police did a great job preventing violence because that's all the news will ever say.

Why is there this need for violence?  Should news stations report the general information even if it's less exciting?