Conflict in greater part of fortification (7)
I believe the answer is:
bulwark
'fortification' is the definition.
(bulwark is a kind of fortification)
'conflict in greater part' is the wordplay.
'conflict' becomes 'war' (war is a kind of conflict).
'in' means one lot of letters goes inside another.
'greater part' becomes 'bulk' (I've seen this before).
'war' going inside 'bulk' is 'BULWARK'.
'of' is the link.
(Other definitions for bulwark that I've seen before include "Rampart" , "Defensive wall" , "defence" , "Fortification - side of ship above deck" , "Buttress" .)