You may want to learn more about the East India Company. If you don't think that an company can start a war then their history may surprise you.
https://en.wikipedia.org/wiki/East_India_Company
Oh I was not disputing they can start wars or even kill, there are examples of such through history. I chose world war as an example of scale and because I was familiar with smaller wars and battles fought by companies. I would still stand by the vast amount of body count difference that government is much more to be feared.
We haven't yet seen a corporation start a world war because multinationals the scale of google and samsung are a relatively recent phenomenon.
With that said I agree that we're unlikely to see a world war started by a corporation. I think we're far more likely to see an interplanetary conflict started by a corporation however.
It will be quite an easy thing for an asteroid mining venture to turn into an arms manufacturer the likes of which we have never seen.
