The remains of fortified archaeological sites abound in hilltop locations on the island of East Timor (Timor-Leste). Archaeologists have linked the emergence of these fortified settlements with environmental change. Some point to a period of reduced rainfall and increased environmental fluctuations beginning about AD 1000, while others cite relatively large-scale climate change during the post-AD 1300 transition from the Medieval Warm Period to the Little Ice Age. Both groups link environmental change to resource unpredictability which in turn leads to inter-group conflict. Of course environmental change is not the only possible trigger for conflict; a variety of social or economic factors could also be responsible. Here we present data on three fortified sites in East Timor, two of which have been dated, and combine these new data with previous work to develop a new chronology for fortifications in eastern East Timor. We then evaluate potential environmental and social factors against this chronology and other archaeological, historical, and ethnohistoric evidence. This assessment indicates that social factors, particularly the impact of increased sandalwood trade, were likely more important drivers of fortification and conflict in East Timor than environmental change.