In Genesis 10 where the table of nations is recorded, we are told in verse 4 that Japheth’s descendants spread out into their territories by their clans within their nations, each with its own language. Also the same is said of Ham’s and Shem’s descendants in verses 20 and 31 respectively. How do we reconcile this with Genesis 11:1 which says, at one time all the people of the world spoke the same language and used the same words?
Genesis 10 is the overview of God’s dispersion of the people and how they were divided. Genesis 11:1-9 explains why it happened. It appears to be in reverse order to us, but it’s similar to the way a news report often gives us the end result of a major event first (the headlines) and then goes back to fill in the details (the story).