God sent Jonah to the city of Nineveh to preach against it. Nineveh was a city that had become very wicked, and God wanted to give the people there a chance to repent and turn away from their evil ways. Jonah was sent to warn them of the consequences of their actions and to call them to turn back to God. Despite initially being resistant to his mission, Jonah ultimately delivered God's message to the people of Nineveh, and they responded by repenting and turning to God.