Numbers 21:29
Woe to thee, Moab! thou art undone, O people of Chemosh: he hath given his sons that escaped, and his daughters, into captivity unto Sihon king of the Amorites. Woe to thee, Moab! thou art undone, O people of Chemosh: he hath given his sons that escaped, and his daughters, into captivity unto Sihon king of the Amorites.
The lament over Moab looks back to an earlier undoing, when its escaped sons and daughters and its territory were given into captivity under Sihon king of the Amorites, a defeat that came before Israel's later victory over Sihon. It stands within the account of Israel's victories over Sihon and Og, in which Israel destroyed the Amorites and took possession of their land. It also belongs to the record that Israel had slain two of the kings of Moab east of the Jordan.
Israel's overcoming of the Amorites was known to Moab and made Moab fear the power supporting Israel. That victory showed Israel to be a powerful people, and when Israel camped in the plains of Moab on this side of the Jordan by Jericho, Balak king of the Moabites and all Moab learned of it and were exceedingly terrified, which moved them to seek help against Israel. That defeat, together with the Lord's miraculous staying of the swollen and impetuous Jordan before Israel, filled the kings of the Amorites and the Canaanites with melting fear.