Why Israel Halted at Ammon's Border After Defeating Sihon

"For the border of the children of Ammon was strong" (Numbers 21:24). And what strength did the border of the children of Ammon have, that they took only up to the border of the children of Ammon — was it its strength? The Holy One, blessed be He, said to him: "And when you come near, opposite the children of Ammon, do not harass them" (Deuteronomy 2:19).