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Mobile pastoralist strategies have evolved over centuries and are well adjusted to the variable climatic conditions of semi-arid regions. However, economic, social, and climatic changes, as well as technical advancements such as truck transportation, have increasingly affected the livelihood of pastoralist households in recent decades. An increase in inequality has been observed between wealthy pastoralists with large herds and impoverished households that are experiencing decreasing herd sizes on the High Plateau in Eastern Morocco, for example. In addition, whereas wealthy pastoralists possess the financial means to use trucks to transport their herds across large distances, the impoverished households are mainly limited to ranges they can travel by foot. This phenomenon can be described as polarization: the emergence of two distinct socio-economic groups with respect to household livestock and monetary resources. The reasons that have led to this polarization, however, are not well understood at present. In this study, we present a multi-agent simulation model to examine the economic, ecological, climatic, and demographic factors driving this polarization. The model captures the feedbacks between pastoralist households, their herds, and the pastures that they use in a common property grazing system. Using this model, we are able to show that heterogeneities in household assets (livestock and monetary resources) are only one cause of polarization. Changes in ecological conditions and the impact of climate and demographic change can also cause polarization, even if households are completely homogeneous in their characteristics.