Other than Nineveh in the time of the prophet, Jonah, there are no other cities in the Bible that acquired a distinct reputation as a city of sin except Sodom and Gomorrah. When God obliterated Sodom and Gomorrah by shrouding them with fire and brimstone, the same thing should have happened to Nineveh. What could have precipitated God’s decision to flatten the two cities?
The details given in the book of Genesis in the Holy Bible are sketchy. It is clear is that God had already passed his initial judgment on Sodom and Gomorrah because of the overwhelming sinfulness of the inhabitants. To check if there were God-fearing people left inside the cities, God sent out two of his angels. He had promised Abraham that if he finds at least ten righteous persons, he will withhold the punishment. The angels found out, however, that the people living in Sodom and Gomorrah had totally debased themselves to the point that they were asking to have sex with men. The homosexuality of the inhabitants and their inhospitality to the angels were the tipping points. With the confirmation done, the judgment became final and was immediately executed. Experts have only found unconfirmed remnants of the cities of Sodom and Gomorrah after God reduced them to rubble and ash.
After what happened to Sodom and Gomorrah, it was almost surprising that God spared Nineveh from his wrath after its people prostrated themselves before him and repented. True repentance led to salvation.