Spelling is Assyrian.
So God did not destroy Nineveh for he had a future plan for the empire, and wanted it to stay strong to punish Israel. Interesting thought.
Certainly God used Assyria to punish Israel. Jonah was about 20 years before the invasion so timeline fits. Still Nineveh still didn't do anything that required God to show mercy or gave a reason why He showed mercy. It is possible that God didn't destroy Nineveh because He planned to use them for the takeover of Israel.
It's not something I considered but certainly interesting idea.
It was a lesson for the people of Israel to learn, as prophets beside Jonah were warning them that they were offending God by their sin. They were trusting in their status as God's chosen people, with the temple in their midst, showing God was dwelling with them.
But
They continued in sin, & rejected the prophets' call to repent.
Read Amos.
Jesus confirmed the account, & used the repentance of the Ninevites who were simply given 40 days warning of destruction, without a "repent or perish" warning to warn the Jews of
this generation. They were given 40 years, with a clear Gospel message.
Mat. 12:38 Then some of the Pharisees and teachers of the law said to him, ‘Teacher, we want to see a sign from you.’
39 He answered, ‘A wicked and adulterous generation asks for a sign! But none will be given it except the sign of the prophet Jonah. 40 For as Jonah was three days and three nights in the belly of a huge fish, so the Son of Man will be three days and three nights in the heart of the earth. 41 The men of Nineveh will stand up at the judgment with this generation and condemn it; for they repented at the preaching of Jonah, and now something greater than Jonah is here. 42 The Queen of the South will rise at the judgment with this generation and condemn it; for she came from the ends of the earth to listen to Solomon’s wisdom, and now something greater than Solomon is here.