For those interested in such matters --

Supersessionists use Joshua 21.43-45 to argue that Israel's Land promises were totally fulfilled at this point in the Biblical narrative, and are thus no longer pertinent with reference to any future fulfillment.

Yet at the end of Joshua's life, in 23.5, he charges "all Israel" to continue on with their efforts to "possess their land, just as the LORD your God has promised you."

There are many other reasons to see Israel's Land promises as ongoing (once we take in the rest of the Biblical narrative with its variegated prophecies and teachings), but even in Joshua's day, the statement could be made that "not one word of all the good promises that the LORD had made to the house of Israel had failed," (21.45) though the outworking of full-orbed covenant fulfillment would take place at God's appointed time. In chapter 21, Covenant fulfillment HAD taken place, but there was more to come.

Many previous and subsequent passages establish the significance and centrality of the Land promised to Abraham (expanded land inheritance in light of Rom. 4.13 doesn't negate the original and specific boundaries, nor the national distinction, by the way) -- written by Psalmists, Prophets/Scribes, NT authors, etc. This underscores the fact that we need to labor to obtain a well-rounded Biblical Theology (taking the whole sweep of Scripture in view), and that we need to understand the Biblical language of "fulfillment" more robustly. - BA Purtle