Moab and Ammon were related as descendants of Lot. Moab might have had a legitimate claim to the land north of the Arnon, which Israel occupied. Sihon, king of the Amorites, had taken this land from Moab earlier (Numbers 21:24). The Israelites conquered Sihon and took over the disputed territory, but Moab did not try to reclaim it. Ammon should not have claimed it either, because the land had never belonged to them.