These were the clans
This refers back to all the people listed in Genesis 10:1-31.
From these the nations separated and went over the earth
"From these clans the nations divided and spread over the earth" or "These clans divided from each other and formed the nations of the earth"
after the flood
This can be stated clearly or more explicitly. AT: "after the flood destroyed the earth" (See: rc://en/ta/man/translate/figs-explicit)