IMO, if the oil prices plunge then the chances of war should decrease. The Saudis are able to make their multi-billion USD defense purchases, only when the oil prices are high. If the brent crude plunges below $20 per barrel and stays there for a few months, then these people would be forced to cut back on their foreign interventions (especially the invasion of neighboring Yemen).
And I personally don't understand how oil price could lead to the war
I mean these countries which rely on oil won't be satisfied with price and get too angry so will attack?
but thats a big loss of value to attack anyone, so I highly doubt that will happen after all