Begins by reminding us of the lands on the east side of Jordan before they crossed the river. It stretched from the River Arnon to Mount Hermon and all the eastern Jordan plain (v1). The two- and one-half tribes were allotted their inheritance there. This was just as much their land.
In verse 6 we are reminded that Moses had defeated two kings on the eastern side. (v2-5) “One was Sihon, king of the Amorites who dwelt in Heshbon and ruled half of Gilead, from Aroer, which is on the bank of the River Arnon, from the middle of that river, even as far as the River Jabbok, which is the border of the Ammonites, and the eastern Jordan plain from the Sea of Chinneroth as far as the Sea of the Arabah (the Salt Sea), the road to Beth Jeshimoth, and southward below the slopes of Pisgah. The other king was Og king of Bashan and his territory, who was of the remnant of the giants, who dwelt at Ashtaroth and at Edrei, and reigned over Mount Hermon, over Salcah, over all Bashan, as far as the border of the Geshurites and the Maachathites, and over half of Gilead to the border of Sihon king of Heshbon.”
Moses had allocated those lands to the tribes of Reuben, Gad and half the tribe of Manasseh. Joshua again gives an overview of the lands and Canaanite nations they had conquered in verses 7 and 8, and then the thirty-one kings conquered (v 9-24). This is history, not myths. Alan Redpath said, “Sometimes in the course of human experience it is good to sit down and reflect on what has been conquered by the grace of God.” Thus, it was good for Israel to recount these facts. This was all behind them and God had done marvellous things for them, but they still had much to do.