This may seem like the truth...
HOWEVER, with the speed and availability of new media. (The internet, blogosphere, TV, etc) and the rapid transmission of information; people today hear about violence around the world, faster, more often, and in full technicolor. So there likely isn't more violence, simply more accessibility to knowledge about said violence.
In the off chance that there IS more violence, more people + same earth = less resources, and more violence per capita.
Food for thought.