2 Chronicles 28:6
For Pekah the son of Remaliah slew in Judah an hundred and twenty thousand in one day, which were all valiant men; because they had forsaken the LORD God of their fathers. For Pekah the son of Remaliah slew in Judah an hundred and twenty thousand in one day, which were all valiant men; because they had forsaken the LORD God of their fathers.
Judah was defeated because its people had sinned by forsaking the Lord God of their fathers. In that judgment Israel struck down many thousands of Judah's valiant men in a single day. Israel also carried away Judah's women and children as captives. God rebuked Israel for intending to enslave their fellow Israelites, and in response they released the captives.