Period of fighting harsh, reflected by American magazine (7)
I believe the answer is:
wartime
'period of fighting' is the definition.
(period of time involving fighting)
'harsh reflected by american magazine' is the wordplay.
'harsh reflected by american' becomes 'war' (I can't justify this - if you can you should believe this answer much more).
'magazine' becomes 'time' (US magazine).
'war'+'time'='WARTIME'
Can you help me to learn more?
(Another definition for wartime that I've seen is " Eg, nineteen thirty nine to nineteen fourty five".)