Senior officers nearly all perished in rebellion (10)
I believe the answer is:
leadership
'senior officers nearly all perished in rebellion' is the definition.
I can't judge whether this defines the answer.
'nearly all perished in rebellion' is the wordplay.
'nearly' means to remove the last letter.
'in rebellion' is an anagram indicator.
'all' with its last letter taken away is 'al'.
'al'+'perished'='alperished'
'alperished' with letters rearranged gives 'LEADERSHIP'.
Can you help me to learn more?
(Other definitions for leadership that I've seen before include "Commander's characteristic" , "Those in charge" , "Best party people" , "Management" , "Had replies (anag.)" .)