Explain what is meant by the frustration-aggression hypothesis

What are the two main beliefs (about frustration and about aggression) that characterize the hypothesis? Furthermore, what does more modern research say about these two conceptual building blocks of the hypothesis? That is, in what ways are they either not true, or are more complex than once thought?

The frustration-aggression hypothesis asserts that aggression stems from the frustration of an individual, who eventually "snaps" when his or her tolerance is reached. The primary beliefs are that 1) all frustration eventually leads to aggression, and 2) all aggression is the product of frustration. As to the first, individuals do not respond only with aggression when frustrated, but may become depressed, or attempt to overcome the source of their frustration. Secondly, apart from the fact that frustration can, indeed, result in aggression, aggression can stem from instrumental causes, like aggression in wartime or in a boxing match.