World War III
Mass destruction could damage much of the Earth, kill many humans, animals and other living things, and cause the collapse of modern civilization. Albert Einstein is often quoted as having said: "I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones". Einstein might not have actually said this, but other things that he said show that he believed the weapons used in World War III might be so devastating that they would end civilization as we know it.