Yayoi society was constantly at war, as historians have known from brief citations about the islands in Chinese annals. For example, of the five thousand skeletons surviving from the Jōmon era, practically none suggests a violent death, whereas among the one thousand skeletons preserved from Yayoi times, about one hundred betray signs of gruesome ends, including beheading and piercing with a dozen or more arrowheads. Iron and stone arrowheads are among the most common finds in Yayoi sites, and by the middle and late Yayoi, iron arrowheads were heavier and more deadly than ever.
Settlement location and structure also imply that Yayoi society was violent. Scattered throughout upland areas, highland settlements for just a few people probably served as lookouts for attackers. Some of these hamlets have pits containing ash, which suggests a system of smoke signals. On the flatlands, one and sometimes two moats with a V-shaped cross section encircle large settlements; as of 1998, about eighty moated villages have been found for the Yayoi period. At Ōtsuka in the Kanto, a trench measured twenty by one hundred thirty meters and was two meters deep. At Ōgidani near Kyoto, there were two ditches one kilometer in length; it is estimated that it would have taken one thousand ten-ton dump trucks to haul away the earth. Many moated settlements also used stakes, twisted branches, and earthen walls as barricades.
Why did the Yayoi resort to war so frequently? The reason is probably related to the importation of agriculture, which, even though it diffused slowly over the archipelago, soon produced classes of haves and have-nots. Villagers resorted to violence when their harvest was inadequate or when they wanted to take over a neighbor’s surplus grain and the lands that had produced them. The discovery of similar moated and walled settlements around the world from an analogous period, when agriculture was just underway, also supports such a view.
The invention of war went along with famine to comprise new ways for agrarian peoples to die. Malnutrition had been a problem under forager regimes, of course, but with the advent of agriculture and the consequent population growth, many more people were dependent on a new subsistence system and liable to starve to death. Known as the “spring hungers,” famine usually beset a family or village whose crop had failed or whose reserves of grain had been exhausted by the late winter. Along with the greater chance of extensive famine came war, which was really just theft organized on a village-wide scale. Every system of subsistence has its advantages and disadvantages.