Form alliance (5)
I believe the answer is:
unite
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">form alliance</span>' is the definition.<br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for unite that I've seen before include "Come together as allies or comrades" , "Become an integrated whole" , "Amalgamate" , "old coin" , "Pull together" .)