Jonah 3:10
Then God saw their works, that they turned from their evil way; and God relented from the disaster that He had said He would bring upon them, and He did not do it.

All of Nineveh repented and God relented.
Some would say this caught God by surprise.
I believe God is all-knowing and, though, He knows what we are going to do, most of the time we don’t. God’s actions often are for our self-awareness.
God is merciful. We stand condemned already because of sin, yet God is ready to give us grace and forgiveness when we ask Him.
We, on the other hand, are a ruthless, unforgiving, unloving, unmerciful race. If you doubt me then turn on the TV and watch one of those true detective or forensic shows and you’ll learn quickly how we treat each other.
I’m sure not everyone in Nineveh was a bad person but there were enough to warrant the destruction of all.
However, God does not want to destroy you. He wants to save you. But like the Ninevites, you must make the first move.