Half of us succeeded, including me (5)
I believe the answer is:
women
'half of us' is the definition.
(roughly half of humanity)
'succeeded including me' is the wordplay.
'succeeded' becomes 'won' (I've seen this before**).
'including' indicates putting letters inside.
'won' enclosing 'me' is 'WOMEN'.
(Other definitions for women that I've seen before include "Adult human females" , "half of our race" , "Ladies" .)