Iron-clad soldiers go in force and open market (4,10)
I believe the answer is:
free enterprise
'open market' is the definition.
(economic term)
'iron-clad soldiers go in force' is the wordplay.
'iron clad soldiers' becomes 'free' (I can't justify this - if you can you should give a lot more credence to this answer).
'go in' becomes 'enter' (synonyms).
'force' becomes 'prise' (I've seen this in other clues).
'free'+'enter'+'prise'='FREE-ENTERPRISE'
'and' is the link.
Can you help me to learn more?
(Other definitions for free enterprise that I've seen before include "capitalist system" , "Economic system" .)