וַיַּ֣רְא אֲרָ֔ם כִּ֥י נִגַּ֖ף לִפְנֵ֣י יִשְׂרָאֵ֑ל וַיֵּאָסְפ֖וּ יָֽחַד׃
And when the Arameans saw that they were put to the worse before Israel, they gathered themselves together.
Read midrashic interpretation of II Samuel 10:15: and classical rabbinic exegesis.