Bert forced to accommodate one ethnic group (5)
I believe the answer is:
tribe
'ethnic group' is the definition.
(I know that tribe is a type of ethnic group)
'bert forced to accommodate one' is the wordplay.
'forced' is an anagram indicator.
'to accommodate' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'bert' is an anagram of 'trbe'.
'trbe' going around 'i' is 'TRIBE'.
(Other definitions for tribe that I've seen before include "Group of related families" , "Israelites' division" , "Traditional social group" , "Native group" , "Breed" .)