Genèse 10:5

From these were distributed the tribes of the islands of the Gentiles, every one according to his language, to his kindred in their nations.

FROM THERE WERE PARTED THE INHABITANTS OF THE MARITIME SETTLEMENT OF THE NATIONS IN THEIR LANDS. The meaning of this is that the children of Japheth are those who dwell on the isles of the sea, and they are separated, each one of his sons residing singly on another isle, and their countries are far from each other. This was indeed the blessing of their father Noah, who said, May G-d enlarge Japheth, meaning that they be numerous in the expanses of the earth. The sons of Ham, however, are all near one another as they dwell on the continents. Therefore Scripture said, And the boundary of the Canaanite was from Sidon…in their lands and in their nations. The same is true of the sons of Shem.
Now Scripture narrates all this in order to inform us of Abraham’s lineage from Shem, and Ham’s descendants are mentioned to inform us of those nations whose lands Abraham was favored with on account of the sin of their fathers. Therefore it tells also of Japheth and of the dispersion in order to inform us of the cause of the difference in languages and the scattering of the nations to the ends of the earth in a short period of time after the first man. Moreover, this narration serves to let us know the kindness of G-d and His keeping the covenant He made with Noah that he would not destroy them.
The Rabbi, Note 139. said in Moreh Nebuchim that the genealogy of the nations verifies to those that hear it the principle of the creation of the world., 11], as would be natural for descendants of one person.” (Ibid., Friedlander’s translation III, p. 273.) This also is true, for our father Abraham will command his children and his household after him and will affirm to them the narration concerning Noah and his sons who saw the flood and were in the ark. Thus he, [Abraham, not having seen the flood but hearing of it], was witness from mouth to mouth in the whole matter of the flood, and he was a fourth witness to creation since Noah saw his father Lamech who saw Adam. Isaac and Jacob saw Shem, the witness of the flood, and Jacob told all this to those that went down to Egypt, as well as to Pharaoh and the people of his generation. The people in every generation similarly know from their fathers who tell them the deeds and progeny of the four to five previous generations.

מאלו נפרדו, after the debacle with the Tower, the descendants of Yaphet chose for themselves the various islands in the Aegean as their habitat, resulting in each tribe being separated from the other.

איש ללשונו, the people on each of those islands developed a different language or dialect. The word הגויים implies that although all these tribes were offspring of Yaphet, they were in fact as if separate nations. Seeing that the descendants of Noach listed comprise a total of 70, the concept of mankind comprising “seventy nations” not including the Jewish people, was born. [If, nowadays, in the United Nations, for instance, we have far more than 70 nations represented, this in no way contradicts the sages’ reference to “the 70 nations of the world.” Ed.]