Subject to popular flee, internal rebellions and diseases, states have historically developed only under very particular agro-ecological circumstances. This paper advances and empirically validates a new perspective on state formation, helping to understand their paucity and uneven development across the globe throughout the pre-industrial era. I posit that the dissimilarity of the agricultural calendar was one of the fundamental constraints for the emergence and persistence of centralised governments. Using data from the Ethnographic Atlas, I provide evidence that the heterogeneity of agricultural growing seasons was a crucial barrier to state centralisation. This holds true when controlling for a wide range of alternative determinants of state-building. The use of potential, rather than observed, agro-ecological data, as well as various robustness tests, give credit to an interpretation of the results beyond the mere correlation. Additional evidence on 19th century taxation in India and China, sheds light on the precise mechanisms whereby crop cycle heterogeneity hindered political centralisation.