When all the kings who were subject to Hadadezer saw that they had been defeated by Israel, they made peace with Israel and became subject to them. So the Arameans were afraid to help the Ammonites anymore.
Jewish Publication Society of America Version (JPS1917) - 2 Samuel 10:19 >And when all the kings that were servants to Hadadezer saw that they were put to the worse before Israel, they made peace with Israel, and served them. So the Arameans feared to help the children of Ammon any more.