Fossil fuel dispute is essentially territorial (4,3)
I believe the answer is:
turf war
'essentially territorial' is the definition.
The definition suggests a singular noun which matches the answer.
'fossil fuel dispute' is the wordplay.
'fossil fuel' becomes 'turf' (I can't explain this - if you can you should give a lot more credence to this answer).
'dispute' becomes 'war'.
'turf'+'war'='TURF WAR'
'is' is the link.
Can you help me to learn more?
(Other definitions for turf war that I've seen before include "Serious horse racing" , "Territorial struggle between gangs" , "contest in which gangs participate?" , "local dispute" , "Dispute over territory between rival gangs" .)