The Hebrew word translated frontier here is different from the one translated “boundary” in verse 18, and can be taken to mean “boundary” or “frontier.” The phrase the sons of Ammon means “the Ammonites,” or “people of Ammon” who, like the Moabites, were descended from Lot (Gen 19.30-38).

For do not harass them or contend with them, see verse 9. The assignment of this region to the Ammonites is stated in the same way as the assignment made to the Moabites in verse 9.

Quoted with permission from Bratcher, Robert G. and Hatton, Howard A. A Handbook on Deuteronomy. (UBS Helps for Translators). New York: UBS, 2000. For this and other handbooks for translators see here .