Earlier, God decreed that each tribe would receive a proportional part of the Land. As the nation makes its way around the Jordan river to enter the land, they have been conquering the local peripheral populations. The tribes of Reuven and Gad see this borderlands and decide that they do not want to enter the land. They approach Moshe and ask if they can live in the trans Jordan area because of their large flocks and the fertile land. This conversation is reminiscent of Lot’s conversations with Avraham in Genesis.

Compare: “The Reubenites and the Gadites owned cattle in very great numbers. Noting that the lands of Jazer and Gilead were a region suitable for cattle” (verse 1)

וּמִקְנֶה רַב הָיָה לִבְנֵי־רְאוּבֵן וְלִבְנֵי־גָד עָצוּם מְאֹד וַיִּרְאוּ אֶת־אֶרֶץ יַעְזֵר וְאֶת־אֶרֶץ גִּלְעָד וְהִנֵּה הַמָּקוֹם מְקוֹם מִקְנֶה

(Numbers 32:1)

and “Lot, who went with Abram, also had flocks and herds and tents / so that the land could not support them staying together; for their possessions were so great that they could not remain together / Lot looked about him and saw how well watered was the whole plain of the Jordan, all of it…” (Genesis 13:8–10).

וְגַם־לְלוֹט הַהֹלֵךְ אֶת־אַבְרָם הָיָה צֹאן וּבָקָר וְאֹהָלִים׃

וְלֹא־נָשָׂא אֹתָם הָאָרֶץ לָשֶׁבֶת יַחְדָּו כִּי־הָיָה רְכוּשָׁם רָב וְלֹא יָכְלוּ לָשֶׁבֶת יַחְדָּו׃

וַיִּשָּׂא־לוֹט אֶת־עֵינָיו וַיַּרְא אֶת־כָּל־כִּכַּר הַיַּרְדֵּן כִּי כֻלָּהּ מַשְׁקֶה

(Genesis 13:6–10)

Moshe is not happy with the request. Possibly there was a sense of frustration considering Moshe would not be able to enter the land and now these tribes are asking to stay outside the land. Moshe makes the tribes promise that they will enter the land and help the rest of the tribes conquer the land before then returning to their new lands across the Jordan river. “The Gadites and the Reubenites answered Moses, ‘Your servants will do as my lord commands.’” (verse 25)

וַיֹּאמֶר בְּנֵי־גָד וּבְנֵי־רְאוּבֵן אֶל־מֹשֶׁה לֵאמֹר עֲבָדֶיךָ יַעֲשׂוּ כַּאֲשֶׁר אֲדֹנִי מְצַוֶּה

(Numbers 32:25)

The two tribes promise two more times. Satisfied with their promises “Moshe assigned to them—to the Gadites, the Reubenites, and the half tribe of Manasseh son of Joseph—the kingdom of Sihon king of the Amorites and the kingdom of King Og of Bashan, the land with its various cities and the territories of their surrounding towns” (verse 33).

וַיִּתֵּן לָהֶם מֹשֶׁה לִבְנֵי־גָד וְלִבְנֵי־רְאוּבֵן וְלַחֲצִי שֵׁבֶט מְנַשֶּׁה בֶן־יוֹסֵף אֶת־מַמְלֶכֶת סִיחֹן מֶלֶךְ הָאֱמֹרִי וְאֶת־מַמְלֶכֶת עוֹג מֶלֶךְ הַבָּשָׁן הָאָרֶץ לְעָרֶיהָ בִּגְבֻלֹת עָרֵי הָאָרֶץ סָבִיב

(Numbers 32:33)

Thirty three verses into the chapter half the tribe of Manasseh appears out of nowhere. Only Gad and Reuven asked to relocate. Why does Moshe split Manasseh? One answer is that Moshe was concerned that having Gad and Reuven on the other side of the Jordan would separate them from their brethren. He therefore had the tribe of Manasseh split over the Jordan river in order to link the two tribes to those in the land. But why Manasseh?

The simple answer could be that Manasseh was the largest tribe. The problem is that Manasseh was not the largest tribe. Manasseh only had around 53,000. Issachar, Zebulun, and Judah were all larger. Judah had the most with 76,000. Why didn’t Moshe split Judah?

Perhaps this was a political move. Judah by itself was the most numerous, but Manasseh and Ephraim together were over 85,000. This would put the sons of Joseph as the largest bloc over Judah, the eventual ruling tribe. To mitigate this, Moshe splits Manasseh. This allows Judah to remain the largest tribe in Israel while also connecting Reuven and Gad to the tribes inside the land.