What does 2 Samuel 21:1 mean?

During David's reign, there was a famine that lasted three years. David asked God about it, and God said, 'It's because of Saul and his family. He killed the Gibeonites.' 2 Samuel 21:1 - Modern Text Bible

(A long famine leads David to seek God's reason, and he learns it's punishment for Saul's violence against the Gibeonites.)