I really liked what @tfloraditch had to say about this. When you read through how he “prophesied” and then sat back to watch everyone hopefully die, it really stands out that Jonah had a bad attitude!
To add to this, the historical significance was that Nineveh belonged to the Assyrians (possibly a capital city), who were enemies to many nations around, and destroyed Israel around 722BC. There is discussion around a pre- or post-exile writing, but Jonah did not want the chance of this enemy repenting.
Another consideration should be made of Jonah’s message. There is discussion around if he really say what God wanted or not, but the message he gave was clear:
Jonah 3:4 NASB
 Then Jonah began to go through the city one day’s walk; and he cried out and said, “Yet forty days and Nineveh will be overthrown.”
What we should remember is that a prophet was only as good as his reputation back in these days. Sometimes simply for profit, sometimes a bad prophecy may cost them their lives:
Deuteronomy 18:20 NASB
 But the prophet who speaks a word presumptuously in My name which I have not commanded him to speak, or which he speaks in the name of other gods, that prophet shall die.’
Jonah was likely more concerned about himself, his hate for his enemies, and not the 120,000+ lives that God had compassion for. The interesting thing is he knew God would not kill them
Jonah 4:2 NASB
 He prayed to the LORD and said, "Please LORD, was not this what I said while I was still in my own country? Therefore in order to forestall this I fled to Tarshish, for I knew that You are a gracious and compassionate God, slow to anger and abundant in lovingkindness, and one who relents concerning calamity.
I really like the book of Jonah. There are so many interesting little details when you start diving into it in relation to what was going on at the time.