Charles Ellicott Commentary 2 Samuel 11:1

"And it came to pass, at the return of the year, at the time when kings go out [to battle], that David sent Joab, and his servants with him, and all Israel; and they destroyed the children of Ammon, and besieged Rabbah. But David tarried at Jerusalem." — 2 Samuel 11:1 (ASV)

After the year was expired. —Literally, as in the margin, at the return of the year. This refers back to 2 Samuel 10:14.

Joab had spent the winter or rainy season at Jerusalem; now he returns to Ammon. David had evidently hurried his campaign against Hadarezer to prevent the junction of his foes, and Joab had probably been sent at first with only a small force to hold the Ammonites in check.

With the speedy and successful close of David’s own operations, he returned to Jerusalem, while the bulk of the army was sent to join Joab. By the curious insertion of a letter, the Hebrew text reads “when angels (or messengers) go forth”. It is corrected in the margin.

Destroyed the children. — 1 Chronicles 20:1 explains wasted the country of the children. After the custom of ancient warfare, while the army was besieging Rabbah, foraging parties were sent out to lay waste the country and cut off any stragglers. Compare to 1 Samuel 13:17–18.