Jonah was angry because he feared God was not just.
I love God's response to Jonah. I'll paraphrase:
God appeals to Jonah's love of nature, pointing out Nineveh contained "many animals." (4:11)
He chases after us when we run away.
He is faithful when we are not.
He consoles us in our deepest fear, anger, and sin.
God reaches into our despair and mess.
He is with us in deathly danger, deathly sin, and deathly thoughts.
It's a battle - a war - against despair.