"In the history of war and society we single out three main innovations to describe significant changes before 1800: the introduction of metal, when humans abandoned stone weapons for ones made from bronze and iron; the domestication of the horse, which gave warriors greater mobility and speed; and the introduction of gunpowder, which transformed war on land and at sea. (Since other parts of the world, such as the Americas, did not have horses until the Europeans brought them in the sixteenth century and some parts of the world, such as Australia, never developed metal weapons, not all human societies have experienced change at the same time.) In each case, of course, many other things were happening both to technology and to society. Metal weapons were only a part of the story: societies had to develop the soldiers and the infrastructures to make use of them. Horses were more formidable when the wheel enabled them to pull chariots or later on when they could carry armed warriors. The introduction of gunpowder too was accompanied by other important developments: in metallurgy, for example, so that guns did not explode when they were fired, or in the design and navigation of ships, so that they could make use of the new cannon."