Many video games involved violent themes. For example, several games involve killing prison guards in order to escape jail. Many young people play video games for hours at a time and concern has been expressed that playing violent video games can lead to violent behavior.
Meta-Analysis of 136 studies of violent video games involving behavior of 130,296 subjects were made. Studies came from both Japan and western countries like USA and Europe. Meta-analysis indicated that more exposure to violent video games was associated with significantly higher rates of violent behavior, higher violent affect, and more anti-social and less empathetic social behavior.
For the full study of the relationships between playing violent video games and aggressive behavior- please see the Anderson et al. article in the March 2010 Psychological Bulletin.