Human society has always been subject to the rise and fall of fortunes. For the tens of thousands of years of pre-history, most human communities lived on the edge of survival. If adequate rains fell at the right time, there was wild food to gather and animals to hunt. If not, there was famine. The rise of agriculture during the late Neolithic Period, or New Stone Age, mitigated the vagaries of nature by allowing for a greater abundance and predictability of food supplies and for the provisioning of larders in times of plenty against times of want. Still, climate could undo the best-laid plans. Prolonged drought could disrupt even advanced civilizations, as appears to have been the fate of the Anasazi in the American Southwest. The Anasazi built complex societies and sophisticated architecture around the turn of the second millennium CE, only to disappear two centuries later as the result of an extended drought and the social unrest it triggered.