Deuteronomy 2:29
(As the children of Esau which dwell in Seir, and the Moabites which dwell in Ar, did unto me;) until I shall pass over Jordan into the land which the LORD our God giveth us. (As the children of Esau which dwell in Seir, and the Moabites which dwell in Ar, did unto me;) until I shall pass over Jordan into the land which the LORD our God giveth us.
Israel was traveling northward toward the promised land after passing to the south of Edom across a vast elevated plain and crossing the brook Zered to the east of Moab. They deliberately did not distress Moab nor contend with them in battle because God had given Ar to the children of Lot for a possession, and the same prohibition protected the Ammonites as fellow descendants of Lot. The Edomites and the Moabites had allowed Israel to pass through their territories, providing the pattern Israel cited to Sihon. Pushing northward, Israel reached the country of the Amorites, a strong and warlike people who had left southern Canaan, crossed the Jordan, warred against Moab, and held undisputed control from the Arnon north to the Jabbok, so the route to the Jordan lay directly through their territory.
Moses sent a friendly message to Sihon the Amorite king at his capital asking peaceful permission to pass on foot by the highway without turning to the right hand or to the left, offering to pay with money for meat and water, with the stated purpose of passing over the Jordan into the land God was giving Israel. That request followed the way of the Edomites and Moabites and intended only to cross the land on foot on the way to the given land. Sihon answered with decided refusal and gathered all the Amorite hosts to oppose Israel's progress, a formidable, well-armed and well-disciplined army that terrified poorly prepared Israel and to all human appearance threatened speedy destruction. Israel's advance toward the Jordan and the given land began with crossing the Arnon and taking possession of the Amorite country after defeating them in battle. The victory was won by the Captain of the Lord's host fighting for His people, the same divine power that would have given Israel victory thirty-eight years earlier if they had trusted Him.