The formation of pre–Silk Road Eurasian empires was driven partly by the spread of northern Chinese broomcorn millet; nano­diamonds and meltglass at Abu Hureyra point to a cosmic impact at the onset of the Younger Dryas; the collapse of Harappan society coincided with the loss of the Ghaggar River’s perenniality and the onset of the Meghalayan Stage; the breakdown of Easter Island society and the cessation of megalithic statue-building postdated European contact; and epigraphic evidence suggested a descent into total war during the Terminal Classic era of Mayan civilization.