Pundits and the press too often treat terrorism and guerrilla tactics as something new, a departure from old-fashioned ways of war. But nothing could be further from the truth. Throughout most of our species’ long and bloody slog, warfare has primarily been carried out by bands of loosely organized, ill-disciplined, and lightly armed volunteers who disdained open battle in favor of stealthy raids and ambushes: the strategies of both tribal warriors and modern guerrillas and terrorists. In fact, conventional warfare is the relatively recent invention. It was first made possible after 10,000 BC by the development of agricultural societies, which produced enough surplus wealth and population to allow for the creation of specially designed fortifications and weapons (and the professionals to operate them).