Business in a brief Federation is asserted positively (8)
I believe the answer is:
affirmed
'asserted positively' is the definition.
'affirmed' can be an answer for 'asserted' ('affirm' can be a synonym of 'assert'). I'm unsure of the 'positively' bit.
'business in a brief federation' is the wordplay.
'business' becomes 'firm' (firm is a kind of business).
'in' is an insertion indicator.
'brief federation' becomes 'fed' (I can't explain this - if you can you should believe this answer much more).
'a'+'fed'='afed'
'firm' going within 'afed' is 'AFFIRMED'.
'is' is the link.
Can you help me to learn more?
(Other definitions for affirmed that I've seen before include "Endorsed" , "Declared solemnly to be true" , "swore" , "Stated positively and firmly" , "Stated emphatically" .)