The Lord commanded Moses to give the sons of Israel instructions for apportioning the land of Canaan. He gave them instructions on the boarders. He appointed Eleazar the priest and Joshua son of Nun as the leaders responsible for apportioning the land among the tribes. The Lord through Moses appointed leaders for each tribe.
Aaron had already died and his son Eleazar had taken over as high priest. Moses would die before the sons of Israel entered the promise land and Joshua would take over from Moses. Caleb was one of the spies who forty years prior spied out the land of Canaan. Caleb and Jacob were the only two remaining from that generation. Joshua was to take over from Moses and Caleb was to be the leader for Judah, but all other tribes had new leadership.
The Lord is the one who was giving them the land and expelling the inhabitance of the land. Therefore, the Lord decides the borders and appoints the leadership. Eleazar and Joshua are the main leaders appointed by the Lord and each tribe was appointed a leader. The apostle Paul wrote: Christ is the head of every man and God is the head of Christ. (1 Cor 11:3)
Jesus said, “All authority has been given to Me in heaven and on earth. Go therefore and make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit, teaching them to observe all that I commanded you; and lo, I am with you always, even to the end of the age.” (Mt 28:18-20
Jesus being our High Priest and King appointed twelve men to make disciples of all the nations, baptizing and teaching. The boarders have expanded to the entire earth and not just a strip of land on the western shore of the Mediterranean Sea.