When Hadadezer’s subjects saw that they had been defeated by Israel, they made peace with David and became subject to him. So the Arameans were unwilling to help the Ammonites anymore.
We may see here, 1. How the hearts of sinners that are marked for ruin are hardened to their destruction. The children of Ammon saw that they had made themselves odious to David (Ch1 19:6), and then it would have been their wisdom to desire conditions of peace, to humble themselves and offer any satisfaction for the injury they had done him, the rather because...
Commenting on 1 Chronicles 19:6-19
They made peace with David, and became his servants - See on Sa2 10:19 (note), and the concluding note in that place; and see for omissions in Chronicles, the preface to these books.
1Ch 19:1-19 The same phenomena are met with in the detailed account of the Ammonite-Syriac war, 1Ch 19:1-2; 1Ch 20:3, as compared with 2 Sam 10:1-11:1, and 2Sa 12:26-31. In 1Ch 19:1 the omission of the name הנוּן after בּנו is merely an oversight, as the omission of the name נחשׁ in 2Sa 10:1 also is.
Commenting on 1 Chronicles 19:1-19