Millions wiped out in heated conflict (3)
I believe the answer is:
war
'conflict' is the definition.
(war is a kind of conflict)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for war that I've seen before include "State of armed conflict" , "State of armed struggle" , "Strife" , "Armed hostility" , "Battle" .)