Frustration-Aggression Theory
First, we need to explain frustration (not that we don't all already know what this is). Frustration is a feeling of tension that occurs when our efforts to reach some goal are blocked. When this occurs, it can produce feelings of anger, which in turn can generate feelings of aggression and aggressive behavior. This theory has been utilized to explain a lot of violent behavior over time. For example, some have stated that people who become frustrated with their jobs because they don't like their work, can't get the raise they want, etc., but can't take out their aggressions at work (can't yell at the boss, can't punch annoying co-workers), will redirect this frustration and act aggressively toward others (like a husband, wife, children, etc.).