Jonah was angry at the Lord for sparing Ninevah, because he told them they were done for and when God relented, Jonah felt his "reputation" was ruined.
I would rejoice if God relented upon His anger and judgement at America.
However, we should also reflect that after Ninevah repented, they went right back to their old ways, and God wiped them out.
That is NOT why Jonah was angry.