Anger seems to be amplified frustration, so the questions are (a) what makes us frustrated, and (b) what amplifies it? It seems that frustration is created by the loss of an object, either property or a person, either a real loss or a fancied or predicted/feared-for loss. We get frustrated and angry in a traffic jam because we are deprived of freedom of movement. We even honk at the "slowpoke" driving in front of us because we are frustrated at our inability to drive faster. Righteous anger is a special category because then we justify our anger by saying that it is directed at a sinner or a breaker of society's laws or mores who therefore deserves both scorn and anger, which may be amplified by our own frustration and anger at never having participated in "sex, drugs, and rock and roll" as the hippies of the '60s did.
It seems that frustration is caused by loss plus the inability to do anything about the loss. (It is notable that in classical psychodynamic theory depression is also caused by a loss. Could the strictures of society then explain why more women than men get depressed, and more men than women get homicidal with rage?) This immediately harkens back to a baby's instant anger when deprived of his/her rattle. Society may have taught us how to channel and not act on the rage we feel from being frustrated, but we have never learned how not to feel frustrated. Giving trophies to all the members of all the little league teams' players rather than just to the winners does not prevent adult feelings of frustration in later life; it just makes the sensation rarer and therefore more difficult to deal with.
So unlike what all mental health practitioners tell us, it is the reaction and negative feeling of frustration that is inborn, and not anger. We must therefore ask what tools our family and society has given us to help us prevent our frustration from exploding into anger, and why, under certain circumstances, our feelings of frustration are relieved by exploding into anger. Of course society accepts our getting furious at ourselves if we drop and break something---we are instantly angry at our loss, and everyone empathizes with us. In a somewhat similar way society understands our getting angry when our favorite team loses, although what it is about the loss that led to our frustration is less clear since in that case nothing tangible was taken from us.
Therefore the thrust of anger management courses should be to teach us how to prevent frustration from escalating into anger, rather than assuming we will get angry and then teaching us how to control it. You should't deal with an alcoholic by teaching him/her how to behave when drunk. By the time we get angry we are already near a dangerous flash point. And it is much more common than we think----boredom, for instance is low-level anger. We are frustrated that we are wasting our time doing whatever it is that is boring us, and then angry at ourselves or others for our not getting up and doing something else. We know deep down that the only thing we have to spend that is uniquely ours is our time, and the time we spend doing something we do not want to do (schoolwork, housework, visiting with inlaws) generates resentment, frustration and eventually anger.
The surest recipe for frustration-amplification-anger is the knowledge that the loss cannot be reversed, thereby adding a feeling of impotence to our frustration. It is all well and good for Omar Khayyam to have written "The moving finger writes.......", but the reality of the irreversibility of time can be a very bitter pill to swallow. Thus when a loved one commits suicide, we become angry because (a) the loved one left us without warning us or seeking permission and (b) it is totally irreversible. Similarly, in a divorce, the children tend to be angriest at the spouse who leaves, no matter what the justification, since it is the act of leaving that certifies the divorce-to-be. In the same vein, when one of a divorced couple gets married, the other spouse and children often get angry all over again because a re-marriage demonstrates to one and all that the marriage is really over.