i think that world war 3 started with the necesity of petroleum of the main countries.
Unlikely, sir. Prices are actually down with fracking, new deposits in arctic by Russia and lifting of iranian embargo.

Because of oversupply and lack of agreements between oil-producing countries members of the OPEC (Saudi Arabia in particular, which pumped at world's records) and also because of lack of coordinated efforts between OPEC and Non-OPEC countries (Russian being a big player, refusing to reduce production) the price of oil fell rapidly in 2015 and continued to slide in 2016 causing the cost of WTI crude to fall to a 10-year low of $26.55 on January 20. The average price of oil in January 2016 was well below $35. Oil did not recover until April 2016, when oil went above the $45 mark.
Countries have been continuously fighting over territories especially those who have oil deposits. They fight for the ownership of it even though it is very far away from them and won't let other country to take over them. Like, you already have resources in your country to begin with so, why do you still want to take other's territories? Just for the things that you can get from it? And after maximizing the things that you can get from it you will leave them afterwards? World War III is really possible if there are countries that will still be continuously greedy of other country's territories.