Deuteronomy 32:8

When the Most High made allotment of the world unto the nations which proceeded from the sons of Noach, in the separation of the writings and languages of the children of men at the time of the division, He cast the lot among the seventy angels, the princes of the nations with whom is the revelation to oversee the city, even at that time He established the limits of the nations according to the sum of the number of the seventy souls of Israel who went down into Mizraim.

The traditional commentators have explained the passage beginning When the Most High allotted inheritances to the peoples as referring to the Generation of the Dispersion [see Sifrey on this verse]. It was during that time that the land became scattered, and it was then that God decreed that the land of the Seven Nations would be Israel’s (and that it would be sufficient to their population — hence, to the number of the children of Israel).

Some people have asserted that set [Hebrew: yaṣṣev] is a verbal noun, like “Lo, I cannot speak [Hebrew: dabber]” [Jeremiah 1: 6]. Others have suggested that it is a verb in the future tense taking the place of one in the past tense, as in “they made a calf in Ḥorev” [Psalms 106: 19]. In my opinion, however, “ask your father” [: 7] and “your elders” [: 7] are references to the learned, and the meaning of the current passage is similar to that in “God has allotted them” [4: 19] — namely, that to every component of the terrestrial world there is a corresponding component in the supernal world. ...

Thus, according to the number of the children of Israel must be understood along the lines of the statement made by our Sages, of Blessed Memory, that the image of Father Jacob is engraved on the Throne of Glory [Midrash Tanḥuma on Numbers 3: 40] — this is a great secret teaching of the Torah. The evidence for this interpretation is the phrase God ’ s share is His people; and it is the greatest of all possible privileges, one which “He has done so for no other nation” [Psalms 147: 20]. This is why Scripture asked “shall you render this to God , O vile and unwise people?” [: 6] — that is, a people that has fallen from eminence through its own wrongdoing. This is the meaning of “your Father, your Owner” [: 6] — i.e., He has acquired you for His glory. He then tutored you, as Scripture will illustrate, in the manner of a father with his son.

בהנחל עליון גוים, when He assigned to them ancestral lands

בהפרידו בני אדם, after the death of Noach and the time of Avraham about which the Torah wrote (Genesis 10,5) “from this point on they separated, branched out by their respective lands, each with its language, etc.” יצב גבולות עמים, twelve descendants of Canaan (Genesis 10,6) mentioned in that context in that chapter of Genesis, corresponding to the eventual 12 tribes of Israel. Canaan and his 11 sons amounted to twelve. (Genesis 10,15-18) The Torah describes the boundaries of the Canaanites as extending from Tzidon in the north to Gerar, near Gaza in the south, and Sodom in the east. This entire region became the land of Israel during the conquest commencing in the days of Joshua, except for the coastal plains inhabited by the Philistines which was conquered many hundreds of years later, and Jerusalem which was captured by David. The Torah does not give details of the boundaries of the territories of any of the other sons of Noach. למספר בני ישראל, matching the number of the Children of Israel.

יצב גבולות עמים, after the tower of Babylon episode, when mankind had lived in a single community, G’d separated them, dividing them up, and established territorial boundaries for the various new nations. Instead of destroying the people who had engaged in building the tower as a challenge to G’d, He did not destroy them as He had the generation of the deluge, but limited their future scope of influence, by assigning only clearly marked territories within which they could be sovereign.

למספר בני ישראל. For the sake of the Children of Israel who were few in numbers, and who would eventually emerge from among these nations. Proof of all this is כי חלק ה' עמו, that G’d has no special claim on any nation other than the people of Israel. All the other nations worship alien deities. Moses explains that had it not been for the fact that G’d knew that the people of Israel would emerge eventually from among one of these nations, He would have wiped out all the people involved in the building of the tower.

בהנחל עליון גוים, “when the Most High gave to the nations their inheritance;”

בהפרידו בני אדם, ”when He separated the children of men;” during the generation of the Tower (Genesis 11,1-11) At that time, due to the confusion of their languages, each “nation,” i.e. the people who had a language in common, moved away from one another and established separate cultures. This occurred due to the direct intervention of G–d as we know from verse 8 in that chapter.

יצב גבולות עמים למספר בני ישראל, “He set the borders of people, relative to the number of the Children of Israel.” He selected the boundaries of the twelve tribes in the land that would be Israel’s in the future. How did He do this? He first allocated the relevant areas to the descendants of Canaan –who were enslaved to the descendants of Shem through Noach’s curse. Seeing that slaves cannot own anything in their own right, they are never more than tenants on that land.- Genesis 10,15-18 lists the genealogy of Canaan, eleven in number, that are relevant in that respect. At least one of the Canaanite families at some point split into two separate families, (“nations”). This was the P’rizi, which therefore has not been listed in the verses we just quoted. The boundaries of the lands occupied by the descendants of Canaan are also spelled out in that chapter in detail. As a result of this we have 12 separate branches of the Canaanite nation matching the 12 tribes of the Israelites at the time of Moses. [Levi did not get an ancestral share, but Joseph, as Yaakov’s firstborn from the wife Rachel he had worked for had two shares, allocated to Menashe and Ephrayim, the sons born to him before Yaakov’s death. The words: למספר בני ישראל, “corresponding to the number of tribes of the Children of Israel,” in our verse make perfect sense therefore.