So the people of Reuben and the people of Gad and the half-tribe of Manasseh returned home, parting from the people of Israel at Shiloh, which is in the land of Canaan, to go to the land of Gilead, their own land of which they had possessed themselves by command of YHWH through Moses.
Joshua 22:9

What God has promised is already your possession whether or not you occupy it at that moment. God's promises are sure. Sometimes we just have to go get them. Sometimes we have to wait for them.

Each of the tribes of Israel didn't keep the spoils from the territory it occupied, but shared in the spoils from the whole land with all of the other tribes. The eastern tribes "parted from the people of Israel at Shiloh". This reflects an unfortunate reality that geographic separation often precedes cultural, religious, and ideological separation.