This happened because King Jeroboam had done many sins. And Jeroboam had caused the people of Israel to do many sins. Jeroboam made the Lord, the God of Israel, very angry.
The people of Judah also sinned {and did} things that the Lord said were wrong. The people did more things to make the Lord angry at them. These people were worse than their fathers that lived before them.
This happened because of all the sins of Baasha and his son, Elah. They sinned and caused the people of Israel to sin. The Lord was angry because they had many idols.