This is a key part of the "song of Moses" commanded and given him by God (note Deuteronomy 31:19) as the children of Israel were about to enter the Promised Land. It is also a key verse in the whole divine plan of God.
It was written about 3,500 years ago, yet even then Moses could speak of the "days of old" and many generations before his time (at least 2,500 years). He also knew about Adam, and that all the people of all those generations had been "sons of Adam." As far as Moses knew by divine revelation, there had been no humans before Adam.
He also mentioned the division of the nations (Genesis 10) that occurred before Israel even existed. Yet somehow these nations were 70 in number, the same as "the number of the children of Israel" when they migrated into Egypt (Genesis 46:27). Israel's "Promised Land" was pre-ordained to be approximately in the hub of all the nations of the whole world that would later come from them.
The apostle Paul also referred to these promised "bounds of the people" when he preached to the intellectuals at the cultural center of the world at Athens in his day, stating that God "hath made of one blood all nations of men for to dwell on all the face of the earth, and hath determined the times before appointed, and the bounds of their habitation" (Acts 17:26-27).
God does have a purpose for every nation and He "preached before the gospel unto Abraham, saying, In thee shall all nations be blessed" (Galatians 3:8). HMM