Here is some information explaining how Americans could become even more aggressive by viewing violence:
Children who have witnessed violence are greatly affected by it. They begin to act out and become angry. It is very hard for children to understand their feelings and how to cope since young children are just learning how to sort out their feelings.
Here is more information and facts about how children cope with war and violence:
After watching so many movies that have violence in them, people can become immune to some of the effects of it after a while. At first when someone sees a violent movie, they grimace and cover their eyes, and may have nightmares about it later. Eventually, after seeing more violence in movies, we can watch it and process it differently. We don't grimace or cover our eyes anymore. We have become calloused.
This can start at a very young age. I found this article which uses children for an example. Please notice the first bullet point in this article: