God defeats his enemies for his sake and for ours. His enemies are our enemies so long as we are his people.
The ultimate fulfillment of the dispossession of the nations from Canaan is still to come. Israel has never fully occupied the land, not even in David's time. Joshua said (Jos 23:4) that the nations that remained in Canaan, not just the land, were part of Israel's inheritance. This is reflected in later prophecies of the Messianic Era when the nations will be defeated or else join with Israel or serve them. Ultimate fulfillment of God's promises concerning the Land of Israel is predicated on faithfulness.
Eventually, Israel will repent and be restored to the Land, and Messiah will complete the removal of God's enemies that Joshua began. As long as God's people remain faithful, they act as his hands and feet in the world and no enemy or force can stand against them. The scale of the mission is irrelevant if we are faithfully acting in God's name.
Joshua 23