The tribes of Gad and Reuben, and half of Manasseh, received their inherited land east of the Jordan River.
As Israel was preparing to enter the land of Canaan, the tribes of Gad and Reuben brought a request to Moses:
1 Now the sons of Reuben and the sons of Gad had a very great multitude of cattle, and they saw the land of Jazer and the land of Gilead; and they saw the place was a place for cattle. 2 So the sons of Reuben and the sons of Gad came and spoke to Moses, to Eleazar the priest, and to the rulers of the congregation, saying, 3 “Ataroth, Dibon, Jazer, Nimrah, Heshbon, Elealeh, Shebam, Nebo, and Beon, 4 the country the Lord delivered over to the children of Israel, is a land appropriate for feeding cattle; and your servants have cattle.” 5 Therefore they said, “If we have found grace in your sight, let this land be given to your servants as a possession. Do not make us cross over the Jordan.”
(Numbers 32:1-5 OSB)
Apparently, Moses perceived this request as an expression of faithless cowardice, for he responded:
6 Then Moses said to the sons of Gad and to the sons of Reuben, “Your brothers go to war, and shall you sit here? 7 Now why do you pervert the minds of the children of Israel from crossing over into the land the Lord gives to them? 8 Did not your fathers act in this way when I sent them away from Kadesh Barnea to spy out the land? 9 For they went up to the Valley of Eshcol and spied out the land; and they turned aside the heart of the children of Israel so they would not enter the land the Lord gave them. 10 So the Lord was very angry that day, and swore an oath, saying, 11 ‘Surely these men who came up from Egypt, from twenty years old and above and who know good and evil, shall not see the land I swore to Abraham, Isaac, and Jacob; for they did not follow after Me, 12 except Caleb the son of Jephunneh, who separated himself, and Joshua the son of Nun; for they followed after the Lord.’ 13 So the Lord was very angry with Israel; and He made them wander in the desert forty years, until all the generation that did evil before the Lord was utterly destroyed. 14 Behold, You rose up in your fathers’ place, a body of sinful men, to increase still more the fierce anger of the Lord against Israel. 15 For you will turn away from Him by again leaving Him in the desert, and you will act lawlessly against this entire congregation.”
(Numbers 32:6-15 OSB)
Whether by clarification of intent or by compromise, the Gadite and Reubenite men committed to fight alongside their brethren:
16 They came to Moses and said, “We will build sheepfolds here for our cattle, and cities for our children; 17 but we will arm ourselves as the advance guard before the sons of Israel until we bring them to their own place; and our children will dwell in the fortified cities because of the land’s inhabitants. 18 Let us not return to our homes until each of the sons of Israel should be distributed to his inheritance. 19 Therefore, let us not inherit with them on the other side of the Jordan and beyond, because we are receiving in full our portions on this eastern side of the Jordan.”
(Numbers 32:16-19 OSB)
Moses warned them sternly:
20 Then Moses said to them, “If you do according to this word, if you arm yourselves before the Lord for the war, 21 and all your armed men cross over the Jordan before the Lord until His enemy is destroyed before His face; 22 and the land is subdued before the Lord, then afterward you shall return, and be blameless before the Lord and before Israel; and this land shall be your possession before the Lord. 23 But if you should not do so, you shall be guilty before the Lord; and you will know your sin when evils overtake you. 24 So you shall build cities for yourselves and for your children, and walled enclosures for your cattle, and do what proceeded out of your mouth.” 25 Then the sons of Gad and the sons of Reuben spoke to Moses, saying, “Your servants will do as our Lord commands. 26 Our children, our wives, and all our cattle will be there in the cities of Gilead; 27 but your servants will cross over, all armed and arrayed for battle before the Lord into the war, in the manner our lord says.”
(Numbers 32:20-27 OSB)
Thus, the deal was struck:
28 So Moses appointed for them Eleazar the priest, Joshua the son of Nun, and rulers of families in the tribes of Israel. 29 Again Moses said to them, “If the sons of Gad and the sons of Reuben cross over the Jordan with you, every man armed for war before the Lord, and you subdue the land before you, then you shall give them the land of Gilead as a possession. 30 But if they do not cross over with you armed for war, you shall carry across their children, their wives, and their cattle before you into the land of Canaan.” 31 Then the sons of Gad and the sons of Reuben answered, saying, “Whatever our Lord says to your servants, so we will do. 32 We will cross over armed before the Lord into the land of Canaan, but you shall give us our possession on the other side of the Jordan.” 33 So Moses gave to the sons of Gad, the sons of Reuben, and the half-tribe of Manasseh, the son of Joseph, the kingdom of Sihon king of the Amorites and the kingdom of Og king of Bashan, the land and its cities with its borders, the cities of the surrounding country.
34 Then the sons of Gad built Dibon, Ataroth, Aroer, 35 Shophan, and Jazer, which they raised up, 36 along with Beth Nimrah and Beth Haran, fortified cities and walled enclosures for sheep. 37 The sons of Reuben built Heshbon, Elealeh, Kirjathaim, 38 and Baal Meon, encircled with walls, and Shibmah; and they named the cities they built after their names. 39 Then the son of Machir the son of Manasseh went to Gilead and took it, and destroyed the Amorites dwelling in it. 40 So Moses gave Gilead to Machir the son of Manasseh, and he dwelt there. 41 Also Jair the son of Manasseh went and took their farming villages, and named them Havoth Jair. 42 Then Nobah went and took Kenath and its villages, and he named them Nobah, after his own name.
(Numbers 32:28-42 OSB)