Genesis 15:16 ASV, Genesis 18:18-24 ASV and Genesis 18:18-33 ASV

I think you see the length of God's grace in the OT in dealing with Sodom. The injustice was too great with so much sex and violence. It must come down. We see back in Genesis 15:16 God's long suffering. The Amorites were bad, but they weren't Sodom-like. This sheds light that when they came back to the Promised Land from Egypt, they were not encountering in battle harmless people, but who for hundreds of years have gotten worse to the point of being Sodom-like.

God will do the exact same thing to Israel many, many years later when they will go down to the depths of being Sodom-like and are devastated by Babylon. Read judges and the rest of the OT to see if God is inequitable in dealing with man's gross sins of sexual perversion, violence and injustice, no matter the country. He's also equally gracious.