To prepare for major conflict, he'd flog water pistols, ridiculously (3,4,3,4,2,3)

'to prepare' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'for major conflict he'd flog water pistols ridiculously' is the wordplay.
I cannot quite understand how this works, but
'conflict' could be 'war' (war is a kind of conflict) and 'war' is found in the answer.
'he'd' could be 'hed' and 'hed' is located in the answer.
'for' could be 'to' (eg both can mean 'in the opinion of') and 'to' is found within the leftover letters.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?