A reason why some people fight (5)

I believe the answer is:

cause

This clue is a double definition.

'a reason' is the first definition.
(I know that cause is a class)

'why some people fight' is the second definition.
(I've seen this before)

(Other definitions for cause that I've seen before include "Grounds" , "Charity - motive" , "Give rise to" , "Bring about" , "why some people fight" .)

I've seen this clue in The Globe and Mail and The Irish News.

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