Adam Clarke on 1 Chronicles 20:1

After the year was expired, at the time that kings go out to battle - About the spring of the year; see the note on 2Sam 11:1.

After this verse the parallel place in Samuel relates the whole story of David and Bath-sheba, and the murder of Uriah, which the compiler of these books passes over as he designedly does almost every thing prejudicial to the character of David. All he states is, but David tarried at Jerusalem; and, while he thus tarried, and Joab conducted the war against the Ammonites, the awful transactions above referred to took place.