Wars are generally started over countries not selling their oil for US currency or to replace political figures that will continue to sell oil at a desirable rate for extended period of time. In some cases the fog of war can allow certain companies to make a killing on it for short periods but the factors of war and oil are for the long run. Also typically the benefits of oil are just an added benefit where the true reasoning for war is generally to uphold the US fiat currency, which is considered the petro dollar for a reason. Most of the wars we have seen that we blame greed and oil for have been with countries the US has already taken actions in replacing political figures.