John Gill Commentary Numbers 21:31

"Thus Israel dwelt in the land of the Amorites." — Numbers 21:31 (ASV)

Thus Israel dwelt in the land of the Amorites. Not the land of the Moabites; and by those means before mentioned; by conquering Sihon their king, they came into the possession of it, and took up their dwelling in it; this was the beginning of the conquest of the Canaanites, and an earnest and pledge of inheriting their land promised unto them; the Israelites that dwelt here were the tribes of Reuben and Gad.