And God isn't a killer, okay.
In the ancient days things were very difficult.
God protected Israel by making them strong and aided them in defeating their enemies. It was either kill or be killed.
God also wanted the Israelites to obey Him and have faith in Him.
And some early cities were so vile that God could no longer tolerate them.
God was also very merciful to the enemies, however.
Read about Jonah, God wanted him to warn the Ninevites of their wickedness so that they might accept the Lord.
Nineveh was the capital of Israel's archenemy, Assyria.
I suggest you discontinue spamming your ignorance, or you should be banned.