God makes an incredible promise to Joshua:
Joshua 1:1 After the death of Moses the servant of the Lord, the Lord said to Joshua son of Nun, Moses’ aide: 2“Moses my servant is dead. Now then, you and all these people, get ready to cross the Jordan River into the land I am about to give to them—to the Israelites. 3 I will give you every place where you set your foot, as I promised Moses.
Still, Joshua's conquest is incomplete:
Joshua 23:4 Remember how I have allotted as an inheritance for your tribes all the land of the nations that remain—the nations I conquered—between the Jordan and the Mediterranean Sea in the west. 5The Lord your God himself will push them out for your sake. He will drive them out before you, and you will take possession of their land, as the Lord your God promised you.
All Joshua has to do is to just go and set foot on the land according to God's promise. Why does he not do it to finish the job?