A lot of activity around military leader becoming target (5)
I believe the answer is:
focus
'target' is the definition.
(I've seen this before)
'a lot of activity around military leader' is the wordplay.
'a lot' becomes 'c'.
'activity' indicates an anagram (letters become active).
'around military leader' becomes 'us' (I can't explain this - if you can you should give a lot more credence to this answer).
'c'+'of'='cof'
'cof' with letters rearranged gives 'foc'.
'foc'+'us'='FOCUS'
'becoming' is the link.
Can you help me to learn more?
(Other definitions for focus that I've seen before include "Adjust camera lenses - concentrate" , "Cynosure" , "Zoom in (on)" , "Bull's eye" , "Point of convergence of light, etc" .)