10:1 -- "These are the generations of Noah's sons"
C. and Japheth
-- "Children were born to them after the flood"
C'. The children of Japheth... (10:2-5)
B'. The children of Ham... (10:6-20)
A'. The children of Shem... (10:21-31)
-- "These are the families of Noah's sons, by their generations, in their nations; from these the nations were dispersed in the earth after the flood."
Walsh then elaborates on the purpose of this literary structure:
[This] sets the parameters for subsequent elaboration, namely all the nations of the world, since all are descended from Noah. By naming Shem first the text assures Israelite readers (who are descended from Shem) that what follows is not irrelevant antiquarian data but is germane to themselves; it then expands the readers' focus from their own people outward to a distant universal horizon. Finally the text narrows the focus to nearer nations and, eventually, to the line of Eber, the eponymous1 ancestor of the Hebrews, and therefore of the readers themselves.2
1. Eponymous refers to naming some thing after a person. In this case, the title of "Hebrew" people is named after Eber, their ancestor among Shem's descendants. The term "Hebrew" (ibrim) shares the same root as Eber (eber).
2. Jerome T. Walsh, Style and Structure in Biblical Hebrew Narrative [The Liturgical Press; Collegeville, MN; 2001] p. 76