דברי הימים א, פרק כ׳, פסוק א׳

The arrival of spring and summer brings a renewal not only to nature but also to the battlefield, as favorable weather conditions allow for the widespread movement of armies. The military campaign against the Ammonites resumes exactly one year after foreign kings had previously marched out to fight Israel and assist Ammon [מצודת דוד, ביאור שטיינזלץ]. This specific season, marked by spring and the harvest, is ideal for warfare because the fields are full of fresh grass, providing abundant food for war horses [רש״י, מלבי״ם]. It is an especially advantageous time for an attacking force. While the local population is forced to flee into fortified cities, the invading army can freely consume the produce of the fields and vineyards. Furthermore, destroying the crops during this season inflicts a devastating double blow to those under siege, condemning them to starvation for both the current year and the year to follow [ביאור שטיינזלץ].

With their Aramean allies no longer supporting them, the small nation of Ammon is left vulnerable. They face a large, highly skilled Israelite army that holds a clear and overwhelming advantage. Joab leads the military forces forward, systematically devastating the Ammonite territory before laying siege to their capital city, Rabbah [מצודת ציון]. Meanwhile, David remains behind in Jerusalem. Given the obvious imbalance of power between the two sides, there is simply no need for the king to personally join the campaign [ביאור שטיינזלץ].

The narrative briefly concludes with Joab striking and destroying Rabbah, but this actually summarizes a much longer and more complex event detailed in the Book of Samuel [מלבי״ם]. The parallel account reveals that Joab initially captured the city's water supply. He then sent for David, urging the king to arrive with the rest of the army to complete the conquest so that the final victory would be officially recorded in David's name rather than his own [רלב״ג, ביאור שטיינזלץ]. Nevertheless, the record here credits the destruction directly to Joab. Even though David arrived at the very end of the battle to claim the formal honor of the conquest, it was Joab who served as the primary conqueror and accomplished the vast majority of the work on the ground [מלבי״ם].