Through this article I contribute to debates about planetary urbanization by specifying how imperialism, defined as states restricting the self-determination of other states or peoples, intersects with urbanization. While recent urban theory has explored how urbanization unfolds at scales beyond the city and in relation to global capital accumulation, it has not fully extended these insights to incorporate the central role of states and imperialism. First, I argue that doing so develops a more expansive account of extended urbanization by revealing how networks of military bases are themselves enmeshed in the production of urban networks via state policies, and that militarized sites safeguard the global capitalist economy that sustains urbanization. Secondly, I argue that imperialism changes concentrated urbanization by restricting self-determination, fomenting spatial formations that prioritize militarism, and shifting urban politics to a larger scale. I show these dynamics through a historical analysis of the US military’s strategic interest in the island of Guåhan/Guam at the end of the second world war, and then generalize from this case to consider variegated outcomes at the intersections of urbanization and imperialism. In the article I aim to more adequately explain the heterogenous ways urbanization unfolds across the contemporary world.