I'm looking for the title and author of a short story where the central plot goes like this. An alien comes to earth and uses his very advanced technology to try to stop war.
First, he disables nuclear weapons. This starts a war with conventional weapons as every superpower is worried about retaining its military supremacy. Then the alien progressively disables more and more primitive weapons, but this only serves to provoke conflicts with even more primitive weapons (guns don't fire, so people use clubs and knives). The alien thus fails, and if I remember correctly he eventually leaves in disgust.