This is the 21st Century. Do you really think wars are just going to be fought using soldiers, "freedom fighters", propaganda, and the like?
Don't forget about the financial side and how the governments have quite a say in many of the biggest multinational corporations. In a world where money is achieving more control than ever before in history, a corporate war could be going on under our very noses, and we wouldn't be any the wiser.
That being said, if a successful "world war" world war does push through, there's a good possibility the next war would be fought with sticks and stones. As corrupt and stupid the politicians are, I doubt they'd want to risk their asses and blow away humanity's development and technology along with their private yachts, designer suits, and sports cars.