In Genesis 11 we are told of the creation of the nations and their languages
Genesis 11:1-9 "And the whole earth was of one language, and of one speech. And it came to pass, as they (Humans) journeyed from the east, that they found a plain in the land of Shinar; and they dwelt there. And they said one to another, Go to, let us make brick, and burn them throughly. And they had brick for stone, and slime had they for morter. And they said, Go to, let us build us a city and a tower, whose top may reach unto heaven; and let us make us a name, lest we be scattered abroad upon the face of the whole earth. And the LORD came down to see the city and the tower, which the children of men builded. And the LORD said, Behold, the people is one, and they have all one language; and this they begin to do: and now nothing will be restrained from them, which they have imagined to do. Go to, let us go down, and there confound their language, that they may not understand one another's speech. So the LORD scattered them abroad from thence upon the face of all the earth: and they left off to build the city. Therefore is the name of it called Babel; because the LORD did there confound the language of all the earth: and from thence did the LORD scatter them abroad upon the face of all the earth."
The Book of Jubilees 10:22-26 "And the Lord our God said unto us: Behold, they are one people, and (this) they begin to do, and now nothing will be withholden from them. Go to, let us go down and confound their language, that they may not understand one another's speech, and they may be dispersed into cities and nations, and one purpose will no longer abide with them till the day of judgment.' And the Lord descended, and we descended with him to see the city and the tower which the children of men had built. And he confounded their language, and they no longer understood one another's speech, and they ceased then to build the city and the tower. For this reason the whole land of Shinar is called Babel, because the Lord did there confound all the language of the children of men, and from thence they were dispersed into their cities, each according to his language and his nation. And the Lord sent a mighty wind against the tower and overthrew it upon the earth, and behold it was between Asshur and Babylon in the land of Shinar, and they called its name 'Overthrow'."
As for the differences in appearance between nations, though scripture does not say so, it would make sense that the Lord also changed their appearnce to further discourage there getting back together as one nation.
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