Anger has many origins within the individual. It may be as a result of childhood abuse; we learn some of our coping skills from our family of origin. Sometimes our environment at work or elsewhere are stressful and by the end of the day we are ready to bite of the head off anyone who aggravates us. The new guy in your former wife's life. The fellow you believe broke up your marriage and took your place as your kids dad. The slow poke on the road, the rude store clerk, the gas tank that was left nearly empty on the work vehicle by the worker from the prior shift. The list of sources can be endless.
Sometimes the anger roots run deep and they are buried in the subconscious mind, like a lion ready to pounce. Many times, the client needs to process the trauma history to reduce or eliminate the anger deep inside.