They were cut out for war (3,8)
I believe the answer is:
the trenches
'they' is the definition.
Both the answer and definition are plural nouns.
Maybe there's an association between them I don't understand?
'cut out for war' is the wordplay.
I cannot really understand how this works, but
'cut' could be 'trench' (I've seen this before) and 'trench' is present in the answer.
The remaining letters 'thees' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'were' is the link.
Can you help me to learn more?
(Another definition for the trenches that I've seen is " First World War excavations".)