Albert Barnes 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 - This refers to the following spring, after the Ammonites had escaped into their city (2 Samuel 10:14).

The children of Ammon - A marginal reference indicates that the text should be read as "the land of the children of Ammon," which is the correct meaning.

David tarried at Jerusalem - With the Syrians subdued, the war against the Ammonites was not important enough to require David’s personal presence. The entire section concerning David’s adultery and Uriah’s death, from this verse to 2 Samuel 12:26, is omitted in the Book of Chronicles.