Tries to include, first, bright people united by descent and language (6)
I believe the answer is:
tribes
'people united by descent and language' is the definition.
I can't judge whether this definition defines the answer.
'tries to include first bright' is the wordplay.
'to include' means one lot of letters goes inside another.
'first bright' becomes 'b' (1st letter of 'bright').
'tries' placed around 'b' is 'TRIBES'.
Can you help me to learn more?
(Other definitions for tribes that I've seen before include "Groups of people related by blood" , "Groups of families in traditional societies" , "Racial groups living in communities headed by chiefs" , "Social groups in traditional societies" , "races" .)