Environment, social processes, and violence are intimately linked but no single type of ecology nor social organization universally promotes violence; people use violence at different times and places for many different reasons. However, it is notable that rates of violence fluctuate over time, often as part of new strategies for navigating changing environments and social organizations. This chapter investigates the frequency of violent behavior in the southern Titicaca Basin from 3000 BC to AD 1600, as shown through skeletal evidence of trauma. Results show two periods during which people experienced significantly more violent trauma. Both of these periods are correlated with low lake levels; however, social factors including ritual, state development, and state collapse also played important roles in determining the probability of violence.