Beginning to stir up endless strife (5)
I believe the answer is:
first
'beginning' is the definition.
(I know that beginning can be written as first)
'stir up endless strife' is the wordplay.
'stir up' indicates anagramming the letters (I've seen 'stirring up' mean this).
'endless' means to remove the last letter.
'strife' with its last letter removed is 'strif'.
'strif' is an anagram of 'FIRST'.
'to' is the link.
(Other definitions for first that I've seen before include "to begin with" , "Rifts of supreme sort" , "Premier (except in football!)" , "Top degree class" , "& 2 Early new year arrivals bringing good luck" .)