Pristine toy soldiers, participants in civil war (3,5,4)
I believe the answer is:
new model army
'participants in civil war' is the definition.
The definition suggests a singular noun which matches the answer.
'pristine toy soldiers' is the wordplay.
'pristine toy' becomes 'newmodel' (I can't explain this - if you can you should believe this answer much more).
'soldiers' becomes 'army' (group of soldiers).
'newmodel'+'army'='NEW MODEL ARMY'
Can you help me to learn more?
(Other definitions for new model army that I've seen before include "Cromwell's fighting force" , "Parliamentarians" , "Civil War parliamentary force" , "Cromwell's fighters" , "Cromwell's well-trained military machine after 1645" .)