Drawing upon modern economic theorists, Guillermo Algaze emphasizes continuous, interlocking, self-reinforcing processes of growth and external trade as keys to "takeoff" toward southern Mesopotamia's regional leadership in the fourth millennium B.C. But the search for historical causality, always complex, would better avoid supposed universals of individual motivation as determinate roots of behavior everywhere and concentrate in the first instance on fuller consideration of the specific context and time. Without denying a role for Algaze's factors, I suggest that ever-present risks of subsistence variability were probably more decisive in encouraging social stratification and a higher degree of regimentation within locally contending city-states there. Enhanced military effectiveness then surely played a part, alongside trade and possibly overshadowing it, in ensuing regional dominance.