No: It's not nuclear weapons. It's not industrialisation. It's not globalisation. Not stock markets. Nor money!
By far the most violent war humans have waged against nature is by coining the term 'meditation'. Nature has designed us in every way to become fidgety, impatient, depressed, greedy, jealous, afraid, lazy... But here we are: lifelong struggling to be that happy and contented soul, perpetually alert, unprovokably non-violent. On the one hand, there's our imaginativeness that makes us believe such a thing is possible. On the other, there're stories of seers, saints, prophets and so on that we embellish and perpetuate through ages with our wishful thinking, which never lets us give up this unending struggle. Could there be anything more violent than this never-ending war waged against one's very own nature?
No: It's meditation. The most violent invention of humankind!