Anger can be compared to weeds in the garden. There are a variety of weeds and each one is unwelcome. Similarly there are many ways in which anger can be experienced. Think of which ones apply to you:

Reflecting on what triggers this anger in us we discover that desire is the one common antecedent. That is:

When we want something and don’t get it, or
When we already have it but fear it could be taken away.

Aversion of course is another form of desire, that of wanting to move away from, rather than towards, the object, person or situation.

Desire can come in many guises, each one seemingly important for our happiness, such as:
The desire for food and drink, sex, money, possessions.

The desire for status, recognition, love, power, position, knowledge.

The desire for comfort, security, achievement.

Of course desire can also lead to other negative emotions like sadness, grief, fear, loneliness, depression and so on.
But some people are more predisposed to the anger cluster of emotions.

There is one more step in our exploration of what causes anger. Consider this analogy:

A handkerchief is made up of threads woven together and each one of those threads is made of spun cotton.
Similarly, anger is born of desire, and each desire is caused by what we think or believe.
So to eliminate anger we need to change the way we think