Humanity has always been violent. Since the time of cavemen, humans have been killing. As time went on, the tools available to humanity solely for the purpose of violence have increased in efficiency. With the easy access to military-grade assault rifles, one person can easily harm many others in a short period of time. In the past, there may have been just as many people with violent tendencies however they were not able to orchestrate violence on such a grand stage.
There is not an increase in violence around the world. It only seems that way because of the advent of social media. We live in an age where any and all world events can be transmitted in an instant. In years past, you could not see or know what you could not access.
Violence has been on the decline around the World for the past several decades. Death caused by violence and wars has been declining substantially. However, a 24/7 news cycle and instant technology increase the amount of news coverage for events like the German hostage taker killed by police. Coverage like this give the appearance that violence is increasing around the World.
Most indicators say that worldwide violence, outside of a few regions, is going down. We are more fearful of violence because it gets more press than it did in the past. The 24-hour news cycle means that outlets need to come up with news all the time. As a result, we think violence is more common when it is less common than ever.