What does 1 Chronicles 20:1 mean?

The next spring, when kings usually go to war, Joab led the army out and devastated the Ammonite land. He surrounded Rabbah, their capital, while David stayed in Jerusalem. Joab captured Rabbah and tore it down. 1 Chronicles 20:1 - Modern Text Bible

(Joab leads a campaign against the Ammonites, destroying their land and capturing their main city, while David remains at home.)