Thematic Bible: The eastern half assists in the conquest of the country west of the jordan river

And the sons of Reuben, Gad, and half the tribe of Manasseh passed over armed before the [other] Israelites, as Moses had bidden them; About 40,000 [of these] prepared for war passed over before the Lord to the plains of Jericho for battle.

And I commanded you at that time, saying, The Lord your God has given you this land to possess it; you [Reuben, Gad, and the half-tribe of Manasseh] shall go over [the Jordan] armed before your brethren the other Israelites, all that are able for war. But your wives and your little ones and your cattle -- "I know that you have many cattle -- "shall remain in your cities which I have given you, Until the Lord has given rest to your brethren as to you, and until they also possess the land which the Lord your God has given them beyond the Jordan. Then shall you return every man to the possession which I have given you.

And to the Reubenites, the Gadites, and the half-tribe of Manasseh, Joshua said, Remember what Moses the servant of the Lord commanded you, saying, The Lord your God is giving you [of these two and a half tribes a place of] rest and will give you this land [east of the Jordan]. Your wives, your little ones, and your cattle shall dwell in the land which Moses gave you on this side of the Jordan, but all your mighty men of valor shall pass on before your brethren [of the other tribes] armed, and help them [possess their land] read more.
Until the Lord gives your brethren rest, as He has given you, and they also possess the land the Lord your God is giving them. Then you shall return to the land of your possession and possess it, the land Moses the Lord's servant gave you on the sunrise side of the Jordan.