Humans are actually a very violent species. It's programmed into all of us. Most of the time it's quiet, latent and hidden deep down inside. Some people even deny it. But it's there all right.
Wars will always happen. You can't fight millions of years of evolution.
We are actually a very loving species. Less than 2% of people are sociopaths and it just so happens that those sociopaths have control over society at the moment.