Cities and states emerged for the first time on the Lower Mesopotamian Plain (LMP) during the Middle Holocene (c. 6000-2000 BCE), reflecting the rise of increasingly complex institutions of bureaucracy and economy, as well as dramatic changes in settlement patterns and social relations. The LMP's physical landscape, geographically coterminous with southern Iraq and southwestern Iran, underwent concurrent and equally radical transformations, as the Tigris and Euphrates established a fertile delta region whose flat terrain was subject to marine transgression and regression. Nevertheless, our understanding of deltaic geomorphology in Sumer has been too low-resolution to model human-environment interactions during urbanization at the requisite spatiotemporal scales. As part of geoarchaeological research programs at the ancient cities of Lagash and Ur, representative of the eastern and western regions of the LMP, this dissertation collected and analyzed sedimentary data to reconstruct and correlate ecological change with the archaeological record. The results, combined with legacy geological reports and digital elevation data, provide critical geomorphological context for understanding the political ecology of city and state formation in the LMP. Specifically, the biogeochemical characterization and dating of sediments have established a complete Holocene deltaic sequence in the Lagash region, showing that the future city-state was underwater during sea level rise until the latter half of the 5th-millennium BCE. Following rapid sedimentation, the delta began its advance south and east over the course of the 4th-millennium, resulting in the environment’s transition from coastal marsh and intertidal mudflat to floodplain. By the end of the first half of the Early Dynastic period, the city and city-state of Lagash lay ever more landwards of the delta’s front. Underlying these transformations was a shift from tide- to river-dominated deltaic architecture. The consequent realignment in the directionality of irrigation regimes from downstream (tidal) to upstream (fluvial) demanded increasing adherence to a poorly timed flood calendar. As a result, agricultural risk increased substantially throughout the 3rd-millennium, leading to an unprecedented investment in landscape engineering through the artificial construction, extensification and maintenance of waterways, along with the establishment and integration of new political communities through historically unique urban institutions related to production and exchange.