19 When the vassals of Hadadezer saw that they had been routed by Israel, they made peace with David and became subject to him. So the Arameans were not willing to help the Ammonites anymore.

Read 1 Chronicles 19:19 Using Other Translations

And when the servants of Hadarezer saw that they were put to the worse before Israel, they made peace with David, and became his servants: neither would the Syrians help the children of Ammon any more.
And when the servants of Hadadezer saw that they had been defeated by Israel, they made peace with David and became subject to him. So the Syrians were not willing to save the Ammonites anymore.
When Hadadezer’s allies saw that they had been defeated by Israel, they surrendered to David and became his subjects. After that, the Arameans were no longer willing to help the Ammonites.