Moshe said to the children of Gad and to the children of Reuben: "Shall your brethren go to the war, and you sit here? Why will you discourage the children of Israel from entering the land which Hashem has given them? Thus your fathers did, when I sent them from Kadesh-barnea to see the land. For when they went up unto the valley of Eshkol, and saw the land, they discouraged the children of Israel from entering the land which Hashem had given them... And, behold, you have risen up in your fathers' stead, a brood of sinful men, to increase Hashem's anger toward Israel." (32:6-14)
What exactly is the problem with Reuven and Gad's request? One possibility is simply that they want to live on the east bank, outside the borders of the promised land. They were rejecting the land of Canaan just as their fathers had.
I find this explanation extremely dubious, for one simple reason. The lands Reuven and Gad requested were recently occupied by the kingdoms of Sichon and Og. If the Israelites went to the trouble and moral complication of exterminating those kingdoms, it can only be because they intended to live there. We personally struggle to justify the Torah's command to kill the Canaanites, by arguing that in their immorality they forfeited their right to live there, that life belongs to God and can be taken away when God desires, that the Israelites needed to live somewhere, and so on. Whether or not these reasons satisfy our consciences in general, none of them would apply to Sichon and Og's kingdoms, if left vacant for some equally immoral Canaanite tribe to occupy. In that case it is inconceivable that the population would be massacred. Rather, we must conclude that some Israelite tribes were destined to live on the east bank.
But if wanting to live on the east bank was OK, then what was the problem with their request? I think it is ONLY that they did not want to fight in the upcoming war to conquer the land of Canaan. (Or at least, Moshe thought that.)
Moshe's specific complaint is: "Shall your brethren go to the war, and you sit here? Why will you discourage the children of Israel from entering the land which Hashem has given them?" His first complaint is about unwillingness to fight. I think the second complaint is a consequence of the first: if these tribes abandon the war, the rest of the people will lose confidence and be unwilling to fight. This, after all was the problem with the spies incident 40 years before. The spies had reported that the land was desirable, but perhaps not conquerable. The people would have happily gone there, but did not have enough confidence and trust in God to begin the battle.
This also fits perfectly with the resolution, in which the tribes agree to fight (as Moshe demanded) and get land on the east bank (as they requested). In the end, everyone gets what they wanted, and we live happily ever after.
The children of Machir son of Menashe went to Gil'ad, and captured it, and dispossessed the Amorites who were there. And Moshe gave Gil'ad to Machir the son of Menashe; and he dwelt there. Yair son of Menashe went and captured its villages, and called them Havot-yair. Nobach went and captured Kenat and its villages, and called it Nobach, after his name. (32:39-42)
Last year I argued that Yair (and perhaps Nobach) did their conquering not in Moshe's time, but decades or centuries beforehand.
I'm undecided as to whether the same is true of Machir. I looked into it a bit, but gave up after deciding that the answer perhaps depended on correct geographical identification of the locations mentioned in the story. Since these areas are all now in Jordan, you can't just look the local hiking map and find the archaeological site next to the modern town of the same name. So I am totally ignorant as to which is near which, which areas were conquered when, where the borders were, and so on. Perhaps someday, depending on your politics, we will either conquer Jordan or be truly friendly and at peace with it. In either case it will be easier to answer these questions. But for now I plead ignorance.
But anyway, returning to Yair's conquering, it seems slightly awkward that it would have happened long beforehand, but be described now without mentioning that it is out of chronological order. To address this point, I think we have to look the larger structure of Sefer Bamidbar.
The end of Sefer Bamidbar is very confusing, with various stories juxtaposed without obvious rhyme or reason. (Though R' Yoni Grossman has a very interesting explanation of the basic structure.) For now I will arbitrarily ignore the Midian and Yehoshua stories and the mussaf and nedarim laws, and just look at the stories which focus on conquest and the inheritance of land.
These stories, listed by chapter, go as follows:
26 Census (for inheriting land)
27 Tzelafchad's daughters
32 Reuven, Gad, Menashe
33 "Masei" - list of travels
34 Borders of Canaan
35 Levite cities, cities of refuge
36 Tzelafchad's daughters again
Even within this series of stories, chapter 33 is deviant. It is not talking about conquest or land, but about the journey. So why did I keep it here while excluding chapters 28 through 31?
I did this because of the clear shift in focus between the stories before and after it. Chapter 32 tells the story of the inheritance on the east bank of the Jordan, while chapter 34 introduces inheritance the west bank of the Jordan. (Chapters 26, 27, 35, and 36 are general and apply to inheritance anywhere.)
Thematically, the sequence is absolutely clear. The unit as a whole is about inheritance. First you start off outside the land of Canaan. While there, you conquer territories such as Gil'ad. But then your journey ends, you reach Canaan, and from now on all your conquering will take place in Canaan. Chapter 33, which tells the definitive story of the 40-year journey which is just now ending, is a major landmark in the Torah. Anything before it relates to the journey outside of Canaan, while anything after it is about the future in Canaan.
The verses we began by quoting, of Yair and Nobach's conquests, are the last verses in chapter 32, and thus the very last verses to tell the story outside Canaan. Admittedly, Yair and Nobach's conquests have little connection to the conquests in Moshe's time. But now, as we finish the story of the journey, we gather together all the random details relating to the east bank (outside Canaan) and record them together. Once you realize that this is not some arbitrary place in the Torah, but rather the very end of a large structural unit, the inclusion of tangential details is easier to understand.
The gemara (Nedarim 22b) says that had Israel not sinned, the only books in Tanach would be the Torah and Sefer Yehoshua. The mention of Sefer Yehoshua indicates that the conquest and settlement of the land of Canaan is an integral part of the Torah's story. It did not make it into the Torah for chronological reasons, but it must be told in the "sequel".
However, the conquest of the east bank does not have this chronological restriction. It appears entirely in the Torah because it happened earlier, in Moshe's lifetime. The stories of Yair and Nobach can (and therefore must) also appear in the Torah, because they too happened before Moshe's death. Their stories are unrelated to any other story, so they necessarily appear somewhat out of place. But as we finish telling the story of the journey and the east bank, their stories must appear, as a sort of appendix.
As a grammatical note, both Yair and Nobach's conquests use the verb "halach" not "vayelech". This may very well be the "past perfect" tense, meaning "they had gone" not "they went". This is a textual indication that we are talking about events in the past, not continuous with the rest of the Torah's story. [The same method is used in Yonah 1:5 and, I believe, Breishit 39:1 and Shemot 24:1, among other places.]
And they journeyed from Kadesh, and pitched in mount Hor, in the edge of the land of Edom. Aharon the priest climbed mount Hor at Hashem's command, and died there, in the fortieth year after the children of Israel left the land of Egypt, in the fifth month, on the first day of the month. Aharon was 123 years old when he died in mount Hor. (33:37-39)
This seems out of place in the list of journeys. It is presumably here because of the first verse of the chapter: "These are the travels of the children of Israel, when they left the land of Egypt by their hosts under the hand of MOSHE AND AHARON." They stop being under Aharon's hand once he dies.
"But if you do not drive out the inhabitants of the land from before you, then those of them that you let remain will be as thorns in your eyes, and as pricks in your sides, and they shall harass you in the land in which you dwell. It shall be that as I thought to do to them, so will I do to you." (33:55-56)
This gives an interesting picture of the interaction between Divine plans and human actions. Driving out the inhabitants is our action, but is called God's plan. If we choose not to drive them out, then God will have "decided" not to implement the plan. And God's next plan, of harassing us, will be carried out by other people.
Food for thought.